Hi Joshi,
If you are using ISU solution, you need to make sure you have applied following note in ERP side first.
2232704 - BUTX FRG0010 403 Tax Classification does not exist
If above note is not your case, please check following KBA carefully.
2172179 - Message no. CRM_PRODUCT_SALES038, Assignment tax for country XX, sequence X, value X is not possible (BP)
Best Regards
Dean Yan