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I’ve stumbled across a rather odd issue where users were starting to complain that all of the sudden they were running a previous version of IE again, even though IE8 had been installed previously in the environment.  Also, they were complaining that when starting IE, it would simply close right after the UI was displayed.  In troubleshooting the issue, we went back and looked at the IE8*.log files and found out that IE8’s setup had been run twice on these machines for some reason (still haven’t figured out why yet – that’s for another day), and had uninstalled IE8 during the second run of the installer!

To see if I could repro this, I built up a set of test VMs running XP SP3 in the environment and installed IE8 in the IE6 and IE7 test VMs, and as expected in both cases I had IE8 installed after the reboot.  I then re-ran the IE8 setup, and it gave me a very odd message – that it was removing “a previous version of Internet Explorer”, rather than trying to install again.  It rebooted the machine after this “removal” finished, and then after logging in as Administrator after the reboot, the IE8 setup continued and installed IE8 again.

Curious now, I recreated the XP SP3 VMs, creating a non-administrative user this time along with the standard Administrator account.  I ran IE8 setup, and as expected I had IE8 installed after the reboot.  I re-ran the IE8 setup, and got the same “removing a previous version of Internet Explorer” message, along with the reboot of the machine after that finished.  At this point, IE on the VM had probably been reverted back to the previously installed version of IE prior to IE8, so I logged on with a non-administrative account to see if the IE8 installation would be retried, and it was not.  Also, the machine had a previous IE6 or IE7 version installed, but any time a user went to open it IE would immediately crash.  Administrators could open IE, but it would not browse to any sites at all (internal or external).

We tried to replicate this on Vista, just to see if it was affecting our Vista users, and it did not repro – instead, when IE8’s setup was run a second time, we got a message that setup had found that the version of IE installed was equal or greater to the version attempting to be installed and that installation would not continue in the IE8.log file.  After debugging the setup further, it appears that because the setup engine on Vista is using WUSA it can’t rollback from IE8, so it logs the warning.

I can’t imagine many people are going to ever run across this in their environments, but it took a good amount of time to figure this out, so I’ll throw this out there so if someone *does* ever run into this, they don’t lose the amount of blood I did while hitting my head against the proverbial wall.