Can confirm upgrading from .12 to .14 and no issues with the database now.
I do think it’s an oversight that no backup is taken of the database before it performs the updates, and simply relies on a successful one from the last backup still being present.
Thanks, updated OP link. 
Thanks for the quick fix. Now do all databases have to be recreated? At least that seems necessary for a backup set which has been complained at in the broken version - the error message also appears for .14 - and so now I am recreating db.
I wonder which db’s are broken now… My db backup is too old. I hope not all db’s have to be rebuilt, because this will take years. I know, my fault, living on the bleeding Canary edge
Not sure I follow? The update process does take a backup, and places it in the same folder as the real database. As it is not possible to proceed with the new database, it is loss-free to simply recover the backup database. If we fix it to give it a better name, it should even be simple to figure out which file to restore.
If you have an existing database (the one for the backup, not the server) and run any operation on it using 2.0.3.13 it will be messed up. So all backups that you have attempted to run with 2.0.3.13 are likely broken. However, as mentioned above and in the other release post it is possible to recover simply by copying in the pre-upgrade database backup.
And much appreciated! If no-one tried the canary, we would hit all the unsuspecting users running the beta releases!
Well for the 3 Windows servers and 1 Fedora server, none of them were left with database backups for the time of the upgrade, they all had backups with the timestamp of the last backup. This was the case for .13 as well.
I skipped .13 so just upgraded directly from .12 and both of my backup jobs worked fine.
I have 2 backups, one local, one remote (pCould) that are both failing when trying to access an external drive (K):
Failed: Invalid path: K:\
Parameter name: path
Details: System.ArgumentException: Invalid path: K:\
Parameter name: path
at Duplicati.Library.Main.Database.LocalDatabase.SplitIntoPrefixAndName(String path)
at Duplicati.Library.Main.Database.LocalBackupDatabase.AddFile(String filename, DateTime lastmodified, Int64 blocksetID, Int64 metadataID, IDbTransaction transaction)
at Duplicati.Library.Main.Operation.Backup.BackupDatabase.<>c__DisplayClass8_0.<AddDirectoryEntryAsync>b__0()
at Duplicati.Library.Main.Operation.Common.SingleRunner.<>c__DisplayClass3_0.<RunOnMain>b__0()
at Duplicati.Library.Main.Operation.Common.SingleRunner.<DoRunOnMain>d__2`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<AddFolderToOutputAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<ProcessMetadata>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<>c__DisplayClass2_0.<<Run>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.BackupHandler.<RunMainOperation>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__19.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at CoCoL.ChannelExtensions.WaitForTaskOrThrow(Task task)
at Duplicati.Library.Main.Controller.<>c__DisplayClass13_0.<Backup>b__0(BackupResults result)
at Duplicati.Library.Main.Controller.RunAction[T](T result, String[]& paths, IFilter& filter, Action`1 method)
Log data:
2019-01-31 07:32:11 -08 - [Error-Duplicati.Library.Main.Operation.BackupHandler-FatalError]: Fatal error
System.ArgumentException: Invalid path: K:\
Parameter name: path
at Duplicati.Library.Main.Database.LocalDatabase.SplitIntoPrefixAndName(String path)
at Duplicati.Library.Main.Database.LocalBackupDatabase.AddFile(String filename, DateTime lastmodified, Int64 blocksetID, Int64 metadataID, IDbTransaction transaction)
at Duplicati.Library.Main.Operation.Backup.BackupDatabase.<>c__DisplayClass8_0.<AddDirectoryEntryAsync>b__0()
at Duplicati.Library.Main.Operation.Common.SingleRunner.<>c__DisplayClass3_0.<RunOnMain>b__0()
at Duplicati.Library.Main.Operation.Common.SingleRunner.<DoRunOnMain>d__2`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<AddFolderToOutputAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<ProcessMetadata>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.Backup.MetadataPreProcess.<>c__DisplayClass2_0.<<Run>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at CoCoL.AutomationExtensions.<RunTask>d__10`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.BackupHandler.<RunMainOperation>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__19.MoveNext()
Worked fine with all prior versions.
Latest canary versions have an issue with root folders as source.
This is a known bug, reported in issue #3637.