The following error appears in the logs
ERROR: [2573-142-52-00000000]Unable to import DataStore '\\<ServerName>\Domino\data\mail\nameofmailbox.nsf' ......Field 'DesignClass' exceeds maximum length of 50.
This is caused by the Template name in the Design Properties of the database being too long.
This could occur for all types of databases. [PABs, Mailfiles and Archives]
To resolve this issue:
1) Edit the template name on all the effected databases
2) Run the Locate Notes Datastores module
3) Check the Design Class section to make sure the newly modified Template name appears correctly. Remove the old Template name.