sounds like your pool is having problems... I have cudaminer running with stratum_proxy and it is working just fine. Verify that your stratum_proxy is working by testing with cpuminer running on 127.0.0.1:8332
Also important is making sure that stratum proxy starts with -pa scrypt e.g. mine looks like:
stratum_proxy.exe -pa scrypt -o fc.altpool.com -p 3333
pause
I was using localhost instead of 127.0.0.1 and I didn't use the -pa scrypt
Will try again later tonight.
Also, the regular stratum proxy doesn't support scrypt, so if you get a message saying that "a" is an illegal port, you are using the bitcoin-only version of the program.