Thank you for your post.
When a record is accessed to be edited/modified, a flag is set for that record to disallow other users to access the record. When the record is committed, the flag is set back to a normal state.
From your description, it sounds like the record you are trying to access had the flag set, but it was never reset (assuming no one else is accessing/modifying the record). Ask the other users to disconnect from the file, close the file and reopen. See if you are then able to access the record.
If this occurs again, try recovering the file (File -> Recover), open the recovered file, and see if you still encounter the same problem.