This error is most likely caused by the Discount analysis being set to the wrong type. Check the default codes assigned to the currency:
Click System, then click Currencies.
Locate the currency code the transaction was originally posted as (for example, GBP) and click the View Record eye icon.
On the Trading Currency record window, click the Defaults tab. Under the Sales or Purchase heading will be all the default Analysis Codes for this Trading Currency.
Locate the Analysis Code from the error and make a note of the Analysis Code type this falls under:
Sales/Purchase Code (Invoices, Credit Notes, Adjustments)
Sales Bank Code (Payments or Receipts)
Sales Discount Code (Remittance or Bulk Receipt where a discount is applied)
The next step is to check the Analysis Code within the Debtors ledger to make sure that the Analysis Code Type is the correct type according to the Sales Defaults from the Trading Currencies window. Click Debtors or Creditors, then click Settings, then click Analysis.
Locate the Analysis and click the View Record, eye icon.
On the Details tab, the Type shows the analysis code's designation.
You cannot change the analysis type while the code is set as a default in the currency record. The simplest resolution is to create new analysis codes of the correct type and update the Currency Defaults.