Ok, for particular infos during ‘3D drivers’ enumerations i need (under GL) to create a temporary RC which is used to give me the vendor implementation and extensions supported… after that everything is cleared clean 
… with this usual sequence (perhaps this is wrong!)
glMakeCurrent(NULL, NULL) ;
if (vrContext !=NULL){
glDeleteContext(vrContext);
vrContext = NULL;
}
if (vrDc != NULL){
DeleteDC(vrDc);
vrDc = NULL;
}
Anyway, when i try to create a brand new RC
after all this enumeration stuff (with a different DC supplied by GetDC(…) that fail
at the SetPixelFormat stage!!! with only the DC value as difference!! 
Any help is welcome… bad headache with that!