If you accidentally try to use a keycard on a keycard reader that has not been set up my game crashes.

I cannot reproduce this. Which SecurityCraft version are you using? Try updating if it's not v1.8.20.1. Always check if you are using the latest version if you want to report a bug. And when reporting crashes, ALWAYS include the crash report, latest.log or debug.log file. It contains this and more information to help us modders to diagnose the issue much more easily.

I am going to close this, as we have fixed this bug way back in March 2019 in v1.8.12 and it doesn't seem to have reappeared since then.