Corrupted & Invalid Viewstate Problem

Hi,

I have installed ASP.Net application on a system.

When accessing the Application from within the LAN, it works fine.

However, when I access the application from the Internet, some pages
gve the following error for VIEWSTATE.

The internal network is protected by a Firewall. My suspicion is that
the problem is due to the firewall. But I do not know how to get thru
this problem.

Please help me out on this. Thanks in advance.

----------------------------------------------------------------------------------

The viewstate is invalid for this page and might be corrupted.

Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: The viewstate is invalid
for this page and might be corrupted.

Source Error:

An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of
the exception can be identified using the exception stack trace below.

Stack Trace:


[HttpException (0x80004005): The viewstate is invalid for this page
and might be corrupted.]
System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +149
System.Web.UI.Page.LoadPageViewState() +18
System.Web.UI.Page.ProcessRequestMain() +423