We see this issue all the time. Right now the leading theory on this is that the PaymentsToday value is updated in AR_OpenInvoice before the Cash Receipt entry is accepted. Then the user either exits the cash receipt entry without accepting it, or their network connection to the Sage server is interrupted and they receive an error that forces them to get out of Sage and log back in. When they go back in, the last Cash Receipts batch they entered is there, but the entry they were working on needs to be re-entered because it was not accepted/saved. When they go to apply the cash, the PaymentsToday value in AR_OpenInvoice reflects the amount entered just before they were forced out of C/R data entry, so they cannot enter a value.
The solution for this is to go into the AR_OpenInvoice table in Datafile Display and Maintenance and reset to the PaymentsToday value to zero.
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Raymond Westcott
MBSG
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