When using Global Changes to set or clear the Week 1 / Month 1 flag, the changes are not applied.
This occurs if your Sage 50 Payroll username contains a space or special character, e.g. "john smith" or "john-smith".
We've resolved this issue from v32.00 of Sage 50 Payroll.
To check your version and install the update, visit the download and install Sage 50 Payroll article.