Symantec Endpoint Protection Manager only manages 11 clients

i have installed symantec endpoint manager on a dell optiplex gx520, which has 2gb of ram, intel pentium 3.4Ghz.I am running xp pro sp3
i have installed and uninstalled clients 3 times. 1st time is because i keep getting unexpected errors on reports.2nd clients would not stay connected. 3rd just to do it again. and it seems that it will never connect more than 11 clients at a time.I have 15 total. The connected clients are never the same unless the computer stays on all the time. I am assuming when clients shut down and turn back on, it is first come first serve up to the limit, 11. Any suggestions.