I did payroll for May last month, printed the payroll summary and loaded payroll.  Didn't touch the system after that.  I logged in today and printed the payroll recon so I can do my journals, then realized the net pay wasn't the same.  

For some reason, the payroll summary of today is different to that which I did in last month.  The tax is more, for 99% of the employees and the UIF is more for all of them.

I did not change anything, nobody has access to the system but me. What happened, what do I do now as my payroll journal is now not balancing in pastel as it seems as if paid everyone too much and did not deduct enough tax/uif?