Transfer Tool - The supplied name is invalid

I am in the process of testing a migration from one WHM server to another. 156 accounts out of 157 pretty much worked fine all apart from one! This one is slightly different to any other though in that it has an addon domain linked to it and the email account is associated with that addon domain. The transfer tool copies it all across, db's, users, addon domain etc, it all looks the same in both Cpanels but the site doesnt work (using Hosts file for the new IP) Accountname is the primary username and i have change the addon domain name to "addondomain" for security This is the error i get: TRANSFER: 1 completed, 0 had warnings, and 0 failed. RESTORE: 1 completed, 1 had warnings, and 0 failed. RESTORE: Account "accountname": Warnings Could not update "/home/accountname/public_html/addondomain/.htaccess": (XID gxbn87) The supplied domain name is invalid. How can i get this account across and working please?