Due to currency exchange rate, Forex gain and loss happened and an error occurred like "Reverse can be made due to entry no xxx". 

This issue can be resolved if you comment-out  a single line code

Table: 179

Method: LOCAL CheckDtldVendLedgEntry(VendLedgEntry : Record "Vendor Ledger Entry") 

Just comment-out below code and reversal can be made then. 

//DtldVendLedgEntry.SETRANGE(Unapplied);

Remember: There may be other consequence for this change. Check carefully before doing comment.