Desktop and taskbar crash after installation

Hello. I had Classic Theme installed some months ago without very much problems. Today I wanted to install it again. But now it doesn't work anymore. I install it via ClassicTheme.exe. It logs me out normally and I log in again. Now something weird is happening. I can see the theme, and I can see the desktop, but after a second it freezes and crashes. The ClassicTheme.exe window opens. I tried it again with Task Manager open and it shows that at the moment, where it crashes, WerFault.exe, userinit.exe and userinit.exe *32 are closing. I don't know these programs, so I have to plan where to put these issues. Does someone know what it could be? I already tried to reinstall the files from the Classic Theme, but it didn't work. Oh, and I saw that the taskbar shortcuts were under the start button from Classic Shell. Uninstalling Classic Shell brought also no success. Can someone help?