Problem solved.My problem is now solved. Here is what should be done.
If you want to force a complete rescan of all the computers that are in your active directory using the active scan do the following.
1. Stop and restart Lansweeper serviceOn the server go to, 
start, select 
administrative tools and the 
services.
Select the service called 
Lansweeper Server.
Right click 
StopRight click 
Start2. Monitor the scanning processOpen your browser and go to: 
http://127.0.0.1:9524/In the Inqueue there should be a list of computers.
If nothing happens and only the server is being scanned. You probably screwed up in the configurations of the Active Scanning.
1. Go to Lansweeper ConfigurationLogin
Go to premium version, active scanning, domain scanning.
Make sure the Enable active scanning is checked
Make sure your Domain DNS name and Domain NetbiosName are correct.
Important: when you add a configuration of DNS and NetbiosName make sur you click the little + sign at the bottom of the screen. If you change a configuration you also have to click the + sign or your modification will not be saved (that was my own problem).
2. How to make sure your DNS and Netbios are correct.Go on one of your active directory server
In 
active directory users & computers right click on your domain name in the tree view.
Click 
properties.
In the 
general tabNext to the gray ICON there is your 
DNS name.Domain name (pre-windows 2000) is your 
Netbios name.I hope this write=up will be usefull to others.