If you can enter car calls ,on ph 2, ind serv, etc., then you are probably right about sec. int. issue. Where do the wires from card reader companies interface box connect to? The wires should come from relay contacts in Card Reader Co.'s control box and feed the card reader inputs on an i/o board of some sort. Otis used addressable MRSEBs,FIBs,RS5s and RS14 boards as interface. Inputs s/b called CRIC01-CRIC08 on an 8 stop job. You may have a bad/intermittant i/o, i/o wiring issue, or bad line termination on i/o board, or hopefully all is well with your controller card reader relays may be intermittantly causing problems. Divorce or override card reader system to isolate.