am able to pass the variables back and forth
between windows(forms in the main and popup windows).
That is not the problem.
--
Problem is
After the pop-up form comes up user enters the value and submits
inside the popup and the value is successfully populated in the main form.
--
Now when the main form is submitted and verified sometimes there are some errors so, the users are instructed to go back and fix them. When user clicks the BACK button, all the entries in the main form are cleared.
THE ENTRIES ARE NOT CLEARED WHEN USER DOESNOT USE THE POPUP.

How do we avoid that?

Thanks

Since so many browsers work differently, and individual settings for caching pages can be changed, there is no way to ensure that all of the data stays in the original form. (when the back button is used)

To keep the data, you would have to pass it all to a new form page. Passing the data to a new page would put everything, including the errors and let the user make the changes they need before submitting it again. So, on your page that tells the user they have errors, give them a "fix my errors" button or some sort of thing. Code that button to a new page where all the entered data is passed forward, thus populating a new form (that looks just like the old one) and have them fix the entries as needed.
If you get creative, you could even flag the incorrect entries to make it easier for the user to remember what needs to be changed.

Check this out.

http://www.google.com/search?hl=en&q=sticky+forms&aq=f&oq=