I have been struggling with this issue since yesterday.
I have been attempting to install the Unity Web Player, Unity Plugin version:
4.1.2f1 on my system which runs Windows 7
However it runs into issues with the install.If I just run the installation program.
Thus I attempted to run the program in Administrator mode and the program appeared to instal. When I tried to open up a a web browser game (with Chrome and Firefox) that required the player it displayed an error lunching unity player and it suggested that I installed it manually.
Knowing that I just installed the program I attempted to uninstall it using the control panel, however the uninstall option did not work.
I Attempted to find the files associated with the program and manually deleted them and attempted to install again.
The the cycle just started over again with the next install.