4 Mhash/s is nearly 0, It will take you a while to get a share. Speed on the website is always a little higher than you will see in GUI Miner.

As for your problem, I don't think it's anything you can fix. It are the pools that are unstable at times. If I check my logs from BTCguild, I have the same error from 17:30 onwards to 18:42. Not much you can do about it except for switching to another pool.