I have a box with two 500 GB drives and Windows 7 installed in 3 partitions ( one partition in one hard drive and two partitions in the other hard drive). I have 2 additional Win7 installations, which I seldom use, so that I can have a failsafe resource to fix systems problems from in my main partition. I tried to install Win7 SP1 in my main partition, but the install failed with an "invalid_data" error. I then installed the "Windows 7 System Update Readiness Tool", per SP1's instructions, but that didn't yield any additional data. Curious, I tried to install SP1 in backup partition 1, which has some software installed, but that got me the exact same result: SP1 failure to install, with the same error reported. Even curioser, I tried to install SP1 in my 3rd partition, which is a spanking new install with zero software installed, i.e., a total software virgin. The exact same result was obtained: SP1 failure to install, with the same error reported. In all 3 partitions, I can update the system just fine via Windows Update...except for SP1. In partitions 1 and 2, I tried the SP1 install with the antivirus (Avast! ) disabled, per tips in several threads at Technet Forums and here. The 3rd partition doesn't have an antivirus installed (it's never used, except to update via Windows Update so I can create a system image to use in case of a dire emergency. I can understand if installing SP1 in a heavily accessed system, with lots of software installed, fails due to whatever reason, but it really blows my mind that SP1 would fail on a FRESH install of Windows 7. Can someone shed some light on this...and possibly provide a tip so I can update my Windows 7 systems to SP1 ? THANKS !