Daniel, could you place here what have you done to solve your problem?
I got the same situation after upgrading to mojarra 2.1.
I've checked web.xml again and again and still having the message 'Illegal attempt...'
Jean, probably you have some wrong library versions! That was my problem
And which one you have together that it's working??
For me any jsf greater than 2.0.3 does not work, so im stuck with this version.