Check your Allowance settings:
Click on Setup, Allowances.
Then look for any Allowances that are not mapped correctly ie. gross / exclude STP reporting group, that have a reporting Subgroup and Other Allowance description.
If so, double click on the Allowance, STP reporting tab, change the Reporting group to Allowance items and select Reporting Subgroup and Other Allowance description.
Close icon to save, click Yes apply to FY.
Then open the Allowance again, STP reporting tab.
Change the Reporting group to what it should be.
Close to save, Yes to Apply to FY.
Click on STP2 reporting and try to STP Update again.