Hi Silvio,
It would be worth checking in the library manager in ArchiCAD to see what files it is trying to load. Do the same on another workstation that you know works fine, and see what differences there are. This option can be found in ArchiCAD under File>Library and Objects>Library Manager.
Generally you would load 3 folders - The standard ArchiCAD library on the workstations' hard drive, the shared office library on the server, and the project specific library also on the server. It may be different on your system.
It may be something weird like it's trying to load the whole contents of the server instead of the individual folders!
Post up a screenshot if you are still having problems.