Error Message Received when trying to post a general journal entry (in this example an Intercompany FX journal entry). 

"Tax Calculation Type must be Sales Tax in Gen. Journal Line Journal Template Name='General', Journal Batch Name='INTERCOMP', Line No.='10000'."
Solution CAUSE:This message occurs if the General Posting Type is incorrect or blank for any of the entries in the journal posting.

SOLUTION:Enter the correct General Posting Type for the type of entry (i.e. Purchase) and post.