Cool, that expression seems to be accepted. I still seem to get the “unable to access” error message though:
The process cannot access the file ‘C:\Work\Projects\~$MyExcelFile.xlsx’ because it is being used by another process. [edit: corrected the missing backslash here]
Also out of curiosity - it occurred to me that selecting to exclude “system files” might also work for this use case, but there’s not much explanation given as to what this will actually exclude (is it only the system-attribute windows files that are hidden by default unless you override them in explorer’s settings) - I’m nervous that checking this option will exclude some specific files that I’d really want to back up, and/or not exclude ones I’d expect to be excluded (such as above) - is there a place with any sort of in-depth explanation for this option?
Edit to add: I tried enabling the setting to exclude System files, and still got this warning - but I checked and the temp file is just hidden, not a system file as far as I can see, and I really don’t want to exclude hidden files from general backup.