focus addClass in IE

focus addClass in IE

hi there,

the following works in FF but not in IE 6 nor IE 7

$('#msgsp').addClass('hidden');

$('#eventname').focus(
function() {
$(this).addClass('input_fields_focus');
}
);

that is IE the div #msgsp is not hidden and when focus on the input box
#eventname the background color aint changed

are there special methods/syntax for IE?
are these methods intended to work in IE?

any help would be appreciated
thx
B