ive had this issue for a while now, but only just got round to investigating it.
On the domain scan my SDP server cant scan any PCs. At first thought it was down to setting/dcom etc. But now ive had chance to play it looks like its the actual data in the database which is the issue!!!
If i do an install of the same version of SDP on a different PC and then scan the domain everything works great. If i uninstall then reinstall and import the backed up data from the live server i cant scan the domain!