Tax is not getting calculated in shopping cart

We are facing a problem where taxes are not getting calculated in shopping cart by Taxware (returning 0.00 for taxable material with no errors), the problem is traced to some errors in jurisdiction codes in R/3, however

1. Any idea about debugging Taxware related issues.

2. The POs those were issued with zero taxes, can we resend/retrigger with updated tax amount to reduce future hassles? or how to synchronize or update tax amount in already issued POs.

Thanks