Is anything listed in the "expenses" tab of that invoice, that's where I always find missing amounts on invoices.  If not, can you view the journal entry (there a button at the top) to show what accounts were affected and by how much?

It's probably not the correct way: but making an invoice to that customer for the same amounts but negative in the same accounts will have the same effect as voiding the original invoice.  Name it "[original invoice number]-v" and apply the old one to the void version.

If this is invoice is for a material amount, maybe run it by the tax accountant first to get their blessing.

You can fix this by going to Reports/Forms/Invoices.  Double click on any of the invoice forms, one in the print screen hit the Refresh button in the upper Right.  That will pull in any Unprinted invoices which just means any without an invoice number.  Hit the Print Email button and it will assign the invoices a number and then you can go into the Receive Money screen and write the invoice off.  Let me know if you have any trouble with it and I could remote in and fix it for you.  [email protected] 

OMG! It work! THANK YOU SOOOOO MUCH!!