Thank you for your post.
I am unable to replicate the issue. This is what I have done:
1. In FileMaker Pro 11.0v4, I created a database file TEST.fp7.
2. I created a Text field "Name", and entered one record with the value "TSGal".
3. I created a script with the following steps:
Set Error Capture [ On ]
Enter Find Mode [ Pause ]
Perform Find [ ]
If [ Get ( Last Error ) = 400 ]
Show Custom Dialog [ "Not a valid entry" ]
Enter Browse Mode [ ]
Exit Script [ ]
Show Custom Dialog [ Get ( LastError ) ]
4. To verify this worked, I ran the script without entering any find criteria, and I got the dialog "Not a valid entry".
5. I ran the script again and entered valid data but not in the database, and I got the dialog 401 (as expected).
6. I launched FileMaker Pro 14.0.4, and migrated the TEST.fp7 file to TEST.fmp12.
7. I ran the script without entering any find criteria, and I got the dialog "Not a valid entry", so I know the Get (LastError) worked properly.
Let me know if there is anything else I can do to replicate the issue.