There can be two causes for this issue:

1. ING Advanced/Rabobank Professional only: go to Components > cciDEAL Virtuemart > Bank Configuration and make sure the value "SubID" is entered (for example "0"). Then make a test payment again. 
2. Otherwise this is a iDEAL system warning (code: SO1000) which means there is maintenance happening on iDEAL. Pause for now and do a test payment again after 5 hours to see if the bank has completed the maintenance.