Each FileMaker file has it's own set of accounts and passwords. I'd check Manage | Security in each of these files and make sure that the same acount in all files is set to the same level of access.
Though I wouldn't grant full access to any user except one permitted to make design changes to the database file itself.
Agreed. Have done this. The actual account I am logged in with has full access and is assigning a record to a lower account but am still getting error messages.
Check each file for damage by taking the file (or a very recent back up copy) and run a recover on them. That will rule out possible issues with the file itself.
Also, test this on more than one computer if possible to rule out issues with a given computer's user accounts. (the accounts managing passwords to access the computer, not FileMaker.)
Thanks Phil and apologies for replying I have been away.