Try following these steps to simply clear a Seed Prepay amount that should go to zero.
1. Go to the Record Payment/Purchase 2. Select the Correct Vendor with this open Prepay. 3. Enter oldest data available for accounting year open, such as 01-01-2016 since you mentioned 2015 has been closed. 4. Go to the Prepay button, select the open Prepay from drop down list. 5. Enter a negative for this open balance (unless you have 2015 prepay for 2016 still listed there, then only enter amount carried over from 2014 not used in 2015). Click OK. 6. Click on the Other expense and payments button. Enter a positive amount for same figure used in step 5. Highlight the match expense account the prepay was setup for and click OK. 7. Total purchase will be zero. 8. Click Record and Done.