I wanted to do a little research on using SQL Server Compact Edition (SSCE) today. I downloaded it and installed it. No problem. I then downloaded the SSCE tools for Visual Studio 2005 SP1. I tried to install these and was greeted with a most unpleasant message:
"The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, or the upgrade patch may update a different version of the program. Verify that the program to be upgraded exists on your computer and that you have the correct upgrade patch."
I was thinking a reinstall of SP1 might be worth it, but that took forever the first time I did it so I didn't want to repeat that process. I started searching the blogs and came across this post by mobility guru Nino Benvenuti. He had a much quicker and easier solution (which he only found after doing a reinstall of SP1 himself):
From the original Visual Studio installation media, locate the \WCU folder and install SQL Mobile from there.
Once I did this, I retried the install and it worked! Thanks Nino -- you saved me a bunch of time!