cannot set the status CLSD

We cannot assign the status Complete (business ) for some Refurbishment orders.

We already run the settlement rule but we received the message below:

"G/L account ABC requires a valid tax code". Please help......

As I have not much dealt with this kind of issues, If feel there is some setting change in the taxcode.

How do I check and compare the tax code and other related setting of this GL and the other..