I have a DB with customers and related DBs tasks and contacts.

Every record has an ID. Customers have a CuID1,CuID2...and so on.

I'd like to know how to avoid duplicate IDs. If I have CuID3 in an otherwise empty DB and I want to add more records starting from CuID1, FileMaker won't skip over the CuID3 it simply creates another CuID3 record without any notices even though I've set the field to UNIQUE. If I manually duplicate a record it works fine (ID+1). I've set the RecordID field to "autoenter serial (+1), unique, prevent modification, etc". How do I avoid the duplicate ID. This is really bugging me since it totally messes up my relationships and I have to sort the mess manually.

Check out CaptKurt's July 24 discussion of unique record IDs and his suggestions in the FileMaker FAQs forum. His method bypasses the problem you describe; a problem, by the way, that will plague you forever using FMP's auto serial number feature.

Sorry, I'm on FMP's side here. If there *was* a CuID1 in the past and it's been deleted then it sould never be re-created again, because it is not unique.

The problem is that people want continuous sequential runs of ID numbers, when really it's only of aesthetic importance.