Note: also asked on Stack Overflow: https://stackoverflow.com/questions/51999057/node-red-catching-error-node-red-contrib-ab
@nsp For the Catch node to work, the node needs to be reporting the errors using the proper API. If you are only getting a log message and nothing from the Catch node, that means the node needs fixing.
However, the node you mention, node-red-contrib-ab has not been updated for 2 years and has no github link associated with it for reporting issues. You would have to contact the author directly to ask if they can make the change.
Alternatively, I see that node is actually an old fork of https://www.npmjs.com/package/node-red-contrib-s7 which is more widely used and actively maintained. You may want to see if you can switch to that module for your particular PLC.