Make sure that SilverFast (incl. the SF_Launcher) doesn't run.
Then try, if deleting SilverFast settings will remedy the issue. In order to do so, you want to delete the "Prefs" folder.
On a typical Windows Vista installation, the SilverFast "Prefs" folder is to be found at:
C:\users\[your username]\AppData\Roaming\LaserSoft Imaging\SilverFast\
If you haven't yet changed the standard setting of the Windows Explorer you won't see any folder "AppData" under your user name, at that point you have to change the folder settings.
In windows explorer press the "Alt" key to see the menu bar, you then want to open the "tools" menu and choose "folder options"; in the new window go to the "View" tab, select the option "Hidden files and folders" and mark the option "show hidden files and folders", you will now be able to see the "AppData" folder and carry on the entire process.
All your specific settings will be lost (saved frame settings, defaults, CMS settings, own Negafix profiles)!
We advise to keep a copy of that folder somewhere else.
