I tried all of the advice but nothing worked for me. I started with two entries of the one customer, one of them with an incorrectly spelled name. I changed the incorrect name but when I tried to merge them the merge would not proceed. I then removed all of the transactions of the incorrectly spelled customer and tried to delete it, but got the message that there was an active transaction somewhere. I could not find anything (as in the descriptions above).  When I tried to change the name of the remaining transaction to the correct spelling, again it will not proceed. I click "OK" but nothing happens. I have to click 'Cancel' to exit. I tried Rebuildig the data with no effect.

Come on Quickbooks. This is clearly a bug. We shouldn't have to pay for you to fix it.