I had this problem with my nachine and it drove me mad. I tried everything to get the thing off, as I had done previously. My machine was due to go for a service as I just do not have the time or the confidence to do it myself, so I took it in for a service and the service technician got the blasted thing off.
How long have you had your Classic? It really needs to go in for a service on a regular basis. At least every 9 to 12 months, depening on how much it is used. Even if its to get the gaskets etc changed and to give it a good clean out.
Also, make sure you descale it with cafetto at least once a month.
If you are in Adelaide pm me and I will give you the contact number of the guy I trust with my machine.