Hi Ashleigh1,
Many thanks for your reply. When I click on Payroll, there are no other tabs showing on the left, but there are 5 (I guess I would call them tabs) across the middle of the screen, labelled Employees, Pay Runs, Approved Leave, Reports, and Payroll Settings.
I tried clearing cache and cookies and then logging off and then on again as you suggested, and then tried again to change the NI cat, but it did the same thing as previously.
However, I noticed that in the "Previous Employer (P45)" section of the screen immediately above the "Save" button, that the right-hand box under "Last entries on P11 Deductions Working Sheet" was outlined in red. The employee had no P45 when they started on our payroll 6 years ago, so that seemed odd. I clicked on the Clear button for the Previous Employer (P45) section, and then tried saving the changed NI cat again, and it worked, their NI Cat change was accepted and saved properly!
Puzzling, but looks like we're set to go now!
Thanks again and regards,
Mike