I had the same problem and it came back often. All the crimps on the cable looked fine to me, but they still didn't seem to work. My only solution was to make a new cable. I bought the parts online and the crimping was much easier than I thought it would be.

See tis post for more info:
http://empeg.comms.net/php/showthreaded.php?Cat=&Board=empeg_general&Number=189530