I don't know Fred and you didn't give any information about your database. Users from all over the world post on this forum to help the fellow user. It's better to comment back on your old post, so everyone will be update and on the same page.
You need a Auto-Enter Serial number field (InvoiceNumber) in your Invoice table. You enter next value to begin with if you don't want to start with 1 and then you enter an increment by number which is 1 by default. Each time you create a new record in the invoice table you will get a new invoice number.
Dear S Chamblee, Thank you for your response. Below was my original question & response.
I think you have posted on the wrong section. This section of the forum is intended for reporting possible software bugs. For assistance in learning how to use FileMaker, please post your question in the FM Pro Forum.
PS : Menu File > Manage Database... and create an auto-enterserial number as shown on my attachment.
I assume you had posted on this forum before because you said you did everything Fred told you, without giving any details. My statement was for information purposes, to help you get your problem solved faster. The more information you can provide the faster a solution can be found.
I gave steps above to fix your problem, which is similar to what Fred suggested to you. If you need any more help with this problem please post here again.