class is a reserved identifier error.....

Hi,

I have installed the activity module, but getting this error in Firebug

class is a reserved identifier
[Break On This Error] for (class in classes) { 

and the activity comments behaviour are unpredictable!!. some comments work correctly.. but for some gives a big error which starts from

An error occurred. <br />/activity/comments/insert<br      .....

and in some comment box after typing comment if i press enter nothing happens.

any guess what's the bug here...? and how to solve this..?