RE: reverse or edit sales tax payment
We came across a similar problem when a user posted the VAT with a completely wrong date. We were able to reverse the sales tax (VAT) voucher using standard GL functionality.
In order to repeat the VAT report calculation you need to look at the table TaxReportPeriod. Access it via table browser and find the right record - you need to filter on Period Type (probably something like 'monthly', 'quarterly') and on the from/to dates. Look at the field VersionNum.
It starts out with the value 0. Then - every time you run a VAT report with update the value is incremented by 1 (so the value 1 after the original posting, 2,3,4... etc when corrections are posted). You will probably see the value 1 in this field. To rerun the VAT report calculation set it to 0 (zero). If you have done corrections the value will be greater than 1 and you can try resetting it to zero to rerun the original calculation. You may need to rerun the recalculations as well.
Note: for India and some Eastern European countries the logic differs so this might not work.
Note 2: make sure you go over this in a test environment before doing it in Prod. Check the original report yields correct results, try posting corrections if you use them. Also try running a vat report in the next month/quarter. You do this at your own risk.
Hope this helps.
Grzegorz