ASP.Net session expired once other tabs are ideal

Hi,

ASP.Net session expired once other tabs are ideal.

example i opened up two tabs one is Item master and other tab is purchase order, once user working more than 20 min in purchase order form then suddenly expired becoz Item master tab session expired and got logged out and clear the session becuase of that while working on purchase order its get logout.

What will be the solution.

Regards,

Basit.