Random Number Duplicate keys

A technique we've used, in the past, is to create a table, on _one_ server that contains the ID's. You want an ID?, you go out to the server and get one. You need to create a table that has your id field, a boolean to indicate if the ID has been used and, possibly, a date field and text field to show who got it, when.

Question:

I am trying to set up documents indices using a random number generator to avoid multiple users getting the same document identifier number. We have two servers, and there is a chance that the same number might appear on each server.

If somehow a duplicate occurs, I will have an “on error” capture. I want to change the duplicate number by adding a random number to the duplicate at the time of the “on error” capture message.

How do I change the document number when it gets captured? Can I go directly from my "on error" capture message to a function that changes the number and have the program continue with that new document number?

Thanks

John