[#NIM086518 ArcGIS Web Adaptor 10.1 SP1 cannot be configured with ArcGIS for Server 10.1 SP1 Site over SSL if the Administrator password has special characters ]
I sure hope this saves at least someone from the headache we went through yesterday. What started out as possibly one of the smoothest SP upgrades to AGS ever quickly turned into long frustrating day. SP1 upgrade for server went fine, SP1 upgrade for IIS Web Adaptor went fine, but simply couldn't register the adaptor no matter how hard we tried.
Fortunately, tech support came across the above bug.
I hope this helps!