Conversion issues.

I am finished entering my historical transactions and - I thought- done setting up my accounts according to my profs instructions. however, I suddenly had to add a whole payroll section, (not yet learned in class but I got through it) and got this message now:

"The sum of yours suppliers information does not equal the balance of account "prepaid expense"

The PP expense isnt for the suppliers, i dont think. what should i do to fix this?