My next suggestion is to go to control panel => add/remove programs and see if that slideshow screensaver is listed. If so; choose to uninstall it.
It could also be in start/ programs and have an option to uninstall the screensaver.
Did you try the registry fix suggested by microsoft?
First you must change the default screensaver to one which is not corrupt such as logon.scr
1. Start Registry Editor (Regedt32.exe).
2. Locate the Scrnsave.exe value under the following registry key:
3. On the Edit menu, click String, type logon.scr, and then click OK.
4. Locate the ScreenSaverIsSecure value.
5. On the Edit menu, click String, type 0, and then click OK.
6. Quit Registry Editor.
If that does not solve it you could try this
If you go to start / run and type regedit and hit enter
Then navigate to
Expand the folder by clicking the plus
Is there an entry (folder) for
ScreenSaver.(whatever the slideshow is called)?
If so, select it and go to file/ export
save that to somewhere like my documents where you can find it later and name it so you will know what it is.
Then again make sure that that one and only that one folder is selected and click edit / delete
or right click on that folder and choose delete
It may also be only under