There is a small bug in an early release of v5.06 which causes a different set of pay elements to appear in the drop-down box on the Payroll screen (e.g. The 'Expenses' element is no longer in the list, instead elements like 'Sun-hol' appear)
If you upgrade to the latest version of Payback (v5.07 or higher) it will fix this problem. Your existing data will not be affected, this is a minor bug which affects the contents of the drop-down list.
Please remember to do a backup before you upgrade! (Admin / Backup / Backup)
The download and instructions are here;
http://www.payback.ie/support.shtml