Tom,
Do you have sufficient free space in your changeinfo directory [N:\changeinfo] to write these files?
Both .info files and .txn files are written to this directory.
The plug-in is reaching the jbacanim.nsf database in the log you provided, is unable to write the changeinfo file, and exits.
If you don't have APP_IGNORE_ERROR set to Y you may want to do so.
This should allow the plug-in to continue in this case and complete with errors.
The error you originally described is occurring because the error occurs in the application unquiesce process.
To make sure that Domino is running properly, when an error is encountered we force an unquiesce.
In this case it doesn't work because the unquiesce has already occurred.
So issue the unable to write info file - the question is why.
It isn't permissions because other .info files were successfully created, so the next best guess that have is there is not available free space.
The .info files are usually pretty small (kbs in size) as they hold information on the changes to the database between the backup start and the backup stop.
Please let us know!
Thanks,
John