Looking over the error message, I think it's the fact that you've specified the directory path. It looks like we now have a "default" directory where we expect to find the file so that part may not be necessary, just the filename itself.
(Optional) Copy the
.tsbakfile to the default file location.
restorecommand expects a backup file in the directory defined in the TSM
basefilepath.backuprestorevariable. By default:
For more information about file paths and how to change them, see tsm File Paths.
So it seems you could either copy your existing backup file to the one default path, or you could change the one variable to define your new default location.