If it's a CWS have you tried CWShredder? I had a system with a CWS and no matter what I did I couldn't remove it using all the methods you described and more. I tried that and sure enough it removed it completely from the system after a couple reboots.
I have since added it to my toolkit just for CWS variants, (in addition to multiple spyware/adware and virus scanners since one never catches everything).
Good luck, adware should be a fricken crime.
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