The problem very probably is caused by a corrupted serial number file. Please be sure to delete it, and then to serialise again.
To delete the serial number file, you need to start SilverFast up using the SF_Launcher. If "start automatically" is activated, the SilverFast plug-in will be started, too. Please close down the SilverFast programme while leaving the SF_Launcher opened.
Using Windows, now press the keyboard combination:
Shift+S+F and click on the "Start" button of the SF_Launcher while keeping the keys pressed. Instead of SilverFast, the "Service Dialogue" window will appear.
Using a Macintosh, please use the combination Alt+Shift+S+F instead and click on "Start" to make the "Service Dialogue" come up.
This will allow you to delete the serialisation, the preferences, or to copy the SF_Logfile to the desktop.
Please note that you need sufficient file permission rights so that the SilverFast service dialogue can succeed in deleting the corrupted file(s).
You therefore want to log-on as administrator (on a Windows system) or root (on a Mac OS X computer).
Note that a Mac OS X admin user may not initially have enough file permission rights, as the admin role on an OS X system means that you can get rights, but do not work all the time with these.
For "how to become root", see another FAQ entry below.