comsat scanner sweep problem

What steps will reproduce the problem?
std::set<BWAPI::Unit*> centers=Broodwar->self()->getUnits();
for(std::set<BWAPI::Unit*>::iterator c=centers.begin();c!=centers.end
();c++){
    if((*c)->getType()==BWAPI::UnitTypes::Terran_Command_Center && 
(*c)->isCompleted() && (*c)->getAddon()->isCompleted())
    {
        if((*c)->getAddon()->getEnergy()>=50)
        {
            (*c)->getAddon()->useTech
(BWAPI::TechTypes::Scanner_Sweep,(*enemy)->getPosition());
            break;
        }
    }
}

this, is my codes to using scanner sweep. but did not work.
What is the expected output? What do you see instead?
detecting any cloaked,burrowed units

What version of the product are you using? On what operating system?
bwapi 2.3.1 , win xp pro sp3, vs2008express sp1

Please provide any additional information below.
BWAPI::UnitTypes::Terran_Comsat_Station is also din't work.

Original issue reported on code.google.com by gg.manag...@gmail.com on 29 Nov 2009 at 9:45

google-code-export / bwapi

comsat scanner sweep problem #147