Don't see any reason why we can't talk in terms of Loads and Lots here.
You should have this relationship: (See Common Forum Relationship and Field Notations Explained if you need help understanding the following notation:)
Loads::__pkLoadsID = Lots::_fkLoadsID
Though your names may differ for these fields, __pkLoadsID should be an auto-entered serial numer field and _fkLoadsID should be a simple number field.
"This action cannot be performed because this field is not modifiable".
indicates that your actions are resulting in FileMaker or you trying to modify a field of type calculation instead of a data field. This could mean you are attempting to directly edit such a field (It could also be that "prohibit modification" was specified), or you have "allow creation of records via this relationship" enabled for Lots, but that the match field you used isn't a simple number field, but rather a calculation field.
Great to discuss in terms of lots and loads - just wanted to use terms that everyone would be familar with.
The Relationship Screen is attached. The following msg will have the Lots layout with field definitions.
Yes, the _pkLoadID field in the Loads table is a auto-enter, serial number field that cannot be edited. See next messag for more info
Attached is the Lots layout and field definitions. When I click in the _fkFieldID field it displays the only record ID in the table as expected. When I click to choose it I get the error message. It apparently is trying to modifiy the LoadID field but I mean to read it in read-only mode. I can replace the shown Pop-up menu field with a basic text-edit field and type in the appropriate LoadID and it works perfectly by displaying the Load Description and Caliber from the Load Table.
This has to be something simple that I'm missing - it's to basic a situation to be anything else.
Thanks a whole lot for your help,
It is something simple.
When I click in the _fkLoadID field...
Take another look at your layout. You aren't clicking the _fkLoadID field, you are clicking into the __pkLoadID field from Loads--the field you have correctly prohibited modification on. Delete this field from your layout and replace it with the _fkLoadId field and it will work.
This fixed the problem exactly as you said and I also get the difference. thanks for helping with the transition...