Hi Clive,
My initial thoughts are to check the file permissions (at the O/S level). On the other hand, it makes no sense that you can update the VOC using ED, or through a Q-pointer from another account, but not from within the account - because the file permissions should the same in all instances.
Does this account use a different LOGIN paragraph? Is there anything in that LOGIN paragraph that will affect user permissions? Is there a security subroutine on the SET.FILE entry in the VOC of the account?
If the worst comes to the worst, then rename the account at the O/S level, and delete it from QM.ACCOUNTS. Then recreate the account, and get a program to recreate the files in the new account and copy the data from the old account. That is a bit tedious, but it should get you a working account.
Cheers,
Brian