Can't Upgrade Because setup & Intallshield Error wont go away.

[MTUSUPPORT]

Run the Disk Cleanup to remove all your Temp Files. You do this by Opening My computer, Right click on the Local Disk C:\ drive. Left click Properties, then click the Disk Cleanup button at the bottom left. It might take a long long time if it has never been run.

If this still doesn't work, then you can search for your Temp directory and manually try deleting the information out of this.