Not sure if you're still having problems, but here's a few suggestions...
A. if you use peerblocker, make sure you add a rule for the pools ip
B. make sure that whatever you put in the password field on the command line is like, i dont know, we'll say 4 or more characters (someone reported connection problems with a single character password earlier today)
C. if you randomly connected earlier after having the problem, and can't figure out what you did to fix it, it was probably not your fault. the pool underwent a very minor attack, it didnt bring the pool down at all but did cause a few brief rpc errors and idle miners for some.
short of that, you could try changing the host to mine1.btcguild.com if you are currently using btcguild.com.
Slush's pool, for one, will get these errors up to 20 times per hour. But this has only been going on for maybe 3-4 days at most.
My miners at BTCG experienced far less, and mostly sporadic rpc errors.
