assign users to group

Hi,

I am facing a problem assigning users to a group I created. I created a group and I am trying to assign a few users to this group. After i select the list of users and press the button select to add them to the group, i get an error message on the screen that says, "exception occured while searching for users."

I don't understand this error message as it has already searched for users and let me even select them and then it throws the error.

i'd appriciate any kind of help, as this is urgent and i can't proceed with out completing this step.

thanks

-smitha