I've been loosing sleep over this, my first filemaker project for customers who think MS Access is better anyway and myself only educated in other rdbms's like Oracle and MS.
My problem, which I had been looking at for quite some time now is how I should connect customers and products-in-stock in an order table. Seems like a easy task but why didn't it work? I tried this and I tried that but no go.
In the end I decided to build a minimalistic solution, only the bare requirements to replay my problem, four tables, four layouts. To be honest I build it to present my problem to you at this forum and hope for someone to solve it. Not very satisfying but ...
Fortunately, my minimalistic solution worked without any problem! I compared both my errorous app and my minimal database and noticed (and fixed!) the problem, something very simple and not filemaker specific at all.
I think that I have been drowned by a lot of filemaker features and concepts. Things like layouts, calculated, summary, resume fields and value lists were and are sometimes overwhelming and can obfuscate the error made earlier. Restrictions can be made in relationships, in the type of field, in the value list and not to mention the things you can do with a script or using triggers.
My point is: Should you have a problem try to re-create that problem using the minimum necessary so you can get a clear view of it. Either you can spot and fix it, or you have a clear example to share here and ask for help.
So; Thank you Filemaker community for helping me fixing my problem.
attached my 'problemsolution', no help needed ....