Hello Thomas,
There is not much information I can give as I have not seen your custom form, and I cannot think of any reason (apart from changes in the form and/or data) that would cause this change in behavior. Some changes that could have been made include:
- Related tables have been added to your data. You will need to enter an ID if the field is being used as part of a relationship key with related tables. ArcPad requires a value for the parent item before it can attach any child records in the related table.
- QuickFields are being used to increment the ID. You can set QuickFields (ArcPad Help) in ArcPad to have auto-incrementing ID's, but you will be prompted for a starting value when you collect your first feature.
- The form has been updated and the ID field has been set as required.
I'm not sure how helpful this is, but I hope it can point you in the right direction.
- Hannah