How do I eliminate the warning message that my extension registration has expired?

   I have been getting the error "The system clock has been set back to the past. This is not allowed!”. How to come out of this problem?
 Can I use a concurrent license for extensions with a single use installation of ArcView or ArcEditor?
 How can I access ARC/INFO for Windows accessing licenses from a UNIX Server.? 
 When I open the Desktop Administrator, I don’t see any folders or options.
 How can I connect to a license server through a firewall?