I faced this error before
java.lang.IllegalArgumentException: Parameter "size" for convert from HTML to java can not be decoded: [11px], reason: Unparseable number:
I know that this will seem not making sense but this problem only happens when running richfaces under Windows with Language set to Arabic. And as I can see from your error trace your Windows Regional Option is set to Arabic so, try changing this setting to maybe English US.
I hope this solves the problem.
[ August 23, 2008: Message edited by: Bassam Al-Sarori ]