Error on backup - System.NullReferenceException


I keep getting this error when I am backupping my machine.

System.NullReferenceException: Object reference not set to an instance of an object
at SharpCompress.Readers.AbstractReader2[TEntry,TVolume].get_Entry () <0x6f8ea60 + 0x00024> in <filename unknown>:0 at SharpCompress.Readers.AbstractReader2[TEntry,TVolume].LoadStreamForReading (System.IO.Stream stream) <0x6f8e8e0 + 0x000ef> in :0
at SharpCompress.Readers.AbstractReader2[TEntry,TVolume].MoveToNextEntry () <0x6f8e798 + 0x0005b> in <filename unknown>:0 at Duplicati.Library.Compression.FileArchiveZip.LoadEntryTable () <0x6e6aa20 + 0x0034f> in <filename unknown>:0 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () <0x18aa010 + 0x00035> in <filename unknown>:0 at CoCoL.ChannelExtensions.WaitForTaskOrThrow (System.Threading.Tasks.Task task) <0x4c28c80 + 0x0009f> in <filename unknown>:0 at Duplicati.Library.Main.Operation.BackupHandler.Run (System.String[] sources, IFilter filter) <0x66b5bb0 + 0x00027> in <filename unknown>:0 at Duplicati.Library.Main.Controller+<>c__DisplayClass13_0.<Backup>b__0 (Duplicati.Library.Main.BackupResults result) <0x66b3148 + 0x000af> in <filename unknown>:0 at Duplicati.Library.Main.Controller.RunAction[T] (Duplicati.Library.Main.T result, System.String[]& paths, IFilter& filter, System.Action1 method) <0x4faac10 + 0x00489> in :0

The backup concerns some Parallels VM on a MacBook Pro.

How do I avoid this and make it take the backup.