Enable some extensions starting with those you think are unlikely to cause an issue (in my case it was a 'Context menu' extension from Boxifier), and repeat steps 3-6 until you have found the culprit.If it is, then continue, otherwise, reenable all extensions previously disabled and continue looking for an alternative solution as this one will not help you.
Here are the steps which worked for me, and not tied to a specific program like WinCDEmu (although it should also fix it). I tried using autoruns from Sysinternals but the latest version as of this writing was very buggy, so I would strongly recommend against using it. I had the same problem and was able to pinpoint the culprit by using the excellent (and free) Shell Extensions Manager by NirSoft.
