Thanks everyone, but I figure it out by myself!
for anyone else who is having this issue, here's the solution:
Please connect or switch on your scanner" appairs when I start ScanWise
connect the scanner with the PC and switch the scanner on.
Start/ Control Panel/ System/ Hardware tab/ Device Manager/ Look for the scanner in imaging devices (scanners/ cameras). If you can see an exclamation mark next to the scanner, this means that the scanner is not installed well.
Click righ mouse button on the scanner, select uninstall to remove the drivers.
Uninstall ScanWise (Start/ Control Panel/ Software)
install ScanWise software again (last Agfa software/drivers: http://www.agfa.com/digicam_scanner_drivers/)
connect and switch on scanner
on Windows XP you can have the warning that this software doesn't have the "digital signature" (Windows Logo test) that XP needs to work properly. You have the choice to continue or stop the installation. Click on the "Continue Anyway" button, the installation will not harm or destabilize your system.