OK - I have more of idea of the problem.
It would seem that I get an error in the Server event log which then stops the Lansweeper Service. I have the service to auto restart, but then it would seem something gets stuck!
As now if I go to http://servername:9524 I don't have anything in the queue and no threads listed as running, but 174 items "In process". Yet this number doesn't appear to change. The Total processes appears to go up very quickly though - almost as though devices are registering with Lansweeper, but no scan is being performed as the queue is stuck.
If I trigger a scan on a device - the machine doesn't appear in the list anywhere either nor does the information update.
Question is - why is this happening and other than a reboot - what will get it going again properly - as it seems the service is running - but "stuck" somehow with these 174 items in process which it can't shift.
The event log in Windows Event Viewer is
EventType clr20r3, P1 lansweeper31.exe, P2 3.2.3160.19571, P3 48b79d61, P4 mscorlib, P5 2.0.0.0, P6 471ebc5b, P7 2976, P8 6a, P9 system.argumentoutofrange, P10 NIL.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.