I was looking at few posts that surfaced by last week on windows phone developer forums around issues relating to the un-install of the CTP we shipped at MIX.
Based on some the information I gathered and the root cause analysis of these, here are some workarounds for the most common issues we saw.
1. When un-installing you are asked to install Silverlight 4 Tools for Visual Studio 2010 RC
Cause for this: Users have installed the Sillverlight 4.0 RTM Runtime after installing Windows Phone Developer Tools - MIX CTP
Workaround: Install the SL 4.0 Developer Runtime and then uninstall the CTP.
2. When un-installing you get a prompt to Install the Microsoft XNA Game Studio 4.0 Windows Phone Extensions.
Cause for this: Very likely you have un-installed the product using Add/Remove Programs
a. Proceed with install of all the listed components.
Then Select the No option in the install source page and click Install to all the listed components when you see this dialog
B. Repeat uninstall. This time the product should uninstall completely
3. A couple of people also noticed this block dialog.
Cause for this: Setup has detected there are some conditions that could get your machine in an bad state and hence prevents the install of CTP Refresh.
a. Some incompatible products/versions are installed as listed. (SL 4.0 SDK, Visual Studio 2010 RC or Beta version, etc)
b. Some process are running that can impact install. E.g. (devenv.exe)
c. or Disk space is not sufficient
Action: Follow the instructions specified in the dialog which will usually be quite explicit about what needs to happens. Like
a. Uninstall the incompatible version of SL 4.0 SDK/Dev10 RC
b. terminate the devenv process if that is running
c. or Free up required space on disk
and then Retry installation, hopefully this should get you unblocked.
You may also want to look at this post by Aaron that talks about setup issues and how to work around them.