Go to the downloadzone to see if there is a new version of the security components.
Disconnect
the card reader and plug it into another USB port. Unplug the USB cable
from the card reader itself, then reconnect it.
If any other reader than the Isabel 6 cardreader is connected to the computer, disconnect it.
Open Internet Explorer (even if you didn't use it)
Click the wrench in the upper right corner> Internet Options > tab Connections > LAN Settings > uncheck the 'Use Automatic configuration script' box
Right-click on the Isabel 6 login icon from your start menu or desktop and select Run as administrator.
Try to login in Isabel 6.
If you can login as administrator, the Windows user rights are insufficient to run Isabel 6.
Correct these limitations in the security or policy configurations.
Make sure that there are no other card readers connected (other than the Isabel card reader).
Verify whether you have a stable connection (the connection may have been interrupted during signing).
Test with another Isabel card reader if one is available (it's possible that your card reader is broken).
Check time and date configuration, follow these instructions.