Problem in Depressurizing Air System.
Try the following:
1. Check the APS for any signs of Ink. Also inspect ALL Ink Cartridges for any signs of leaking (the bottom valve of the Ink Cartridge will contain ink).
2. If there is ink leakage, replace ALL Ink Cartridges, the APS and the Tubes System.
Only replace one component at a time and check if the error has gone before replacing another component. Using this procedure you will be able to determine exactly which component failed.