Two things:

1) Go in there and make DAMN sure you didn't typo something in that one guy's macro (I've done it. Don't argue. Cut&paste macros into notepad and compare them that way; you can't always tell wtf is wrong in WoW's retarded fonts.)
2) Target something with your main and wait 5 seconds, then cast CL. If it works with an artificial delay, you're running into the "ping-pong" delay and there's not much you can do about this but wait a second or two until the packets catch up.

If you've tried both of the above and still no joy, try typing each part of your macro into the command bar of your alt and see if it works individually. This is the only real way to debug which part of it isn't working. Would also help if you pasted your macro in here straight from your macros_cache.txt file.