Error message 'System.IO filenotfound exception: could not load file or assembly 'ProclaimMTD' Version 1.0.0.1' authorising user in VAT Management
This looks like an error on the system with not having the correct files installed, suggest that you should have a full install on the desktop this relates to to make sure all files are available to use.
If the VAT return is urgent then try logging onto a different server or using another users PC to submit.
If Access would normally do the install then please raise a new case online and reference reinstall.