Error message on aplication of Invoice

Orun

Hi !

In Customer master of NAV 2013 R2, application method under Payment first tab is set to 'Apply to Oldest'. When a customer has open invoice (posted with Service Tax) entry and user wants to post another fresh invoice with service tax, system is throwing error message " Invoice with service tax can't be applied against an invoice"

Not only that if customer has any open entry (no Service tax) with document type 'Payment' same error is appearing during new invoice posting.
We found that in Code unit 12 the error message has been mentioned.

Please provide solution.