If you want to provide db for analysis, follow instructions at bottom of my post.
How to attach file: http://www.accessforums.net/showthread.php?t=70301 To provide db: copy, remove confidential data, run compact & repair, zip w/Windows Compression.
I absolutely guarantee that Refresh or F5 did not cause your field to become read only.
Your FK field will not be an autonumber so it won't be created automatically.
I expect this is from a table that is on the many side of a 1 to many relationship and you have deleted the corresponding record in the '1 table'
Do you know about how referential integrity works?