Kaustubh,
One way to make it easier to determine the issue is to have a user that can submit log on to a machine where the user has been having problems and have them submit.
If the submit is successful then the issue with the user. If it does not work then it is an issue with the machine. Compare successful vs non- successful workstations versions
of Office and Internet Explorer. Also check the settings in IE between both workstations.
Let me know if this helps to narrow it down.
Pete