Gravity Forms Eway Pro v1.13.1 has been released. It fixes a fatal error with some old form configurations with invalid properties.
Since tightening up variable types in the PHP code, every now and then another weird one pops up, and it has again. Some old forms have a Credit Card field with an old version of the accepted cards data, as an empty string instead of an empty array. This caused a fatal error on a website after update recently, so I’ve given it the defensive programming treatment and now check that it’s an array before using it. Sorry!
You can update to the latest version from your WordPress plugin admin page. Here’s the full changelog for Gravity Forms Eway Pro.