I have a client computer that is giving me this error. I’m using XPSP2, IE8 and Java 6U18.
I’d start looking at general computer problems on that machine - out of hard drive space, ram-check, etc. Also make sure the IE cache isn’t full and clear the Java cache for good measure. Lastly you could try clearing the cache under %USER_HOME%/.ignition/ but I don’t think this could be the cause because if those files were corrupted they would fail the CRC check and get re-downloaded.