i would check what Brewski mentioned but it goes even farther than that. Check the condition of the contactor itself, if it's worn out it can effect the way the tips make and break even with new tips. A worn armature in the contactor can cause it to hang up or bind not allowing the tips to move freely and if this occurs the tips will not contact each other well triggering the code 23 or 24.

Defective 1A, RB, SP or FW contactors can also trigger this code, an open motor circuit between A1 and A2 also can trigger this code. Check for open circuit or loose connection between positive side of RB contactor coil and PB2 on control card. Check the terminal connections at the plug on the control card as well, you can also use some needle nose pliers and put a slight twist on the pins to insure they will make a positive connection with the plug.