Barry, using CAT5 cable is quite common practice for RS232. However an absence of shield can be critical in some cases, ie. when you can not avoit of running signal and communication cables side by side on a long distance. RS-232 works with 10V levels, and can induce quite some unwanted noise currents in paralel signal cabling.

pnnielsen, maybe the communication was too fast, and data got lost. RS232 (at least in my experience) is transmitted rarely at higher speeds than 19200 baud (which is the official standard upper speed). Those higher baud rates were developed for modems etc, and are not really standard.