I had this same problem and spent hours on the phone with SE customer support (which did no good). In short, they had me reinstall the game about 4 times and I also ended up reformatting my Hard Drive. I thought there was a problem with my HDD but it turned out that it was just a new update to my Spyware and Anitvirus Program that caused the problem. I am currently updating my system as I type this and it is working fine ever since I uninstalled Spyware Doctor and Antivirus. I'll reinstall them after the updates are done.
If you don't have a program interferring with the update, then you may have a corrupt Hard Drive that you would need to replace.