Server volumes may be connected to the file system with different protocols (AFP, SMB, FTP, etc.). Whether or not it is possible to drag & drop files located on the server volume directly into timeSensor LEGAL will depend on this protocol.
Under Mac OS X, the server volumes from which you wish to drag & drop files from into timeSensor LEGAL should be connected with AFP protocol. If that is not the case, you will need to copy the files on the desktop first and archive them from there.
If you do not know under which protocol your server volumes operate, select the volume, then go to "File" and select "Get Info". In the information window, you will find the information you are looking for right next to the server's IP address. You may consider asking your IT administrator to connect the server volume with AFP.