Can't get the diffuser back in the machine after being cleaned. ?

I've just descaled and cleaned my machine, but I can't get the diffuser back in. I have been trying now for hours and am absolutely at my wits end with it. Has anybody else had this problem? I have had the machine about 2 years so I am used to putting it in and out of the machine and have never had this problem before

Linda P
January 2012