Rename/delete the files named SqlCe35AddinStore.sdf and SqlCe40AddinStore.sdf located in C:\Users\your name\AppData\Local (%appdata%).
Also make sure you have either SqlCe 4.0 or 3.5 properly installed.
The issue here was that the 3.5 installtion was broken, I will also attempt to improve the check for the precense of 3.5