and found this;
http://sherylcanter.com/wordpress/2008/12/another-installation-already-in-progress-but-its-not/
I can't be sure this is the right way to go, so you may want to see what others say.
The link above tells how to disable the "Windows Installer Service", reboot, (Restart), the computer, then re-enable the service.
You may want to double check your system doesn't have any malware infections with the two free anti-malware scanners, Malwarebytes' Anti-malware and SUPERAntiSpyware
I hope that helps.
Mark
When I am trying to install a program (any program), it usually installs it to about 70% and then stops, telling me that another installation is taking place and that I must stop that other installation before installing the program that I want (for example, itunes or the associated files).
What do I need to do to stop that other installation from taking place? I called Dell but I'll be damned if I'm paying 130.00 to have this answered.

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