Firstly welcome to the forums.
Secondly the Optional Sponsor is not installed if you did not choose it.
Look familiar? This would have been the sponsor installation agreement you would have agreed to.
Now Messenger Plus! does not interfere with the installation of any other programs so the fact that you cannot uninstall it has nothing to do with other applications. Now if you cannot uninstall Messenger Plus! you want to make sure of a few things.
You are the User who installed it
You have Administrative Access
And all Internet Explorer windows are Closed
If these are all ok and it still will not uninstall please reinstall the Beta of Messenger Plus! with the Sponsor program and then feel try to try and uninstall it again. If it is successful feel free to install it again without the Optional Sponsor program. You can get the Beta from
here.
Feel free to post again if you need more help.