I lost 40 customers in the beginning of this year. I deleted all old customer accounts and now I only have 24 customers in my list. All looks good except from the home screen when I click on Apply Payments box OR go to the payments on the ribbon, the drop list show the 60+ people I had before.
I checked the Customers folder in C:\ProgramData\NCH Software\ExpressInvoice and there are only the 24 customers like it is supposed to be.
Nevermind I figured it out.... since some of my old customers had credits, I ended up deleting all files here C:\ProgramData\NCH Software\ExpressInvoice\CreditNotes
This brought my Apply Payment list to my current customer list.
I hope this can help someone else.