Weird error when trying to update inventorydetails

[Guido1982]

For the module I'm developing I'm trying to update inventorydetails through the normal save method (and setting focusmode to edit). Saving new records is fine, but updating existing records causes:

Code:

Sorry! Attempt to access restricted file.
We are looking for this file path: modules//.php
We are looking here:
Real file path:

Any idea why this is?