This error can have different causes and solutions and appears when a user is trying to make a payment in the iDEAL environment. Please try the following solutions to fix it. 

 Reinstall cciDEAL

• Remove cciDEAL from the website (Extension > Install/Uninstall > Components)
• Install the latest version of cciDEAL
• Make sure all configuration details are still correct (Components > cciDEAL)
• Make a new test payment and check to see if the error is fixed

• Please check that the key in the Rabobank Dashboard (TEST and PRODUCTION) are the same as the key inserted in cciDEAL under bank configuration
• We advise you to completely delete this key, add a new one in the Rabobank Dashboards (TEST and PRODUCTION) and also add this key to the cciDEAL bank configuration
• Make a new test payment and check to see if the error is fixed