ASP.net web application SSRS Report issues on Server 2008 R2 IIS 7.5.

We have upgraded our windows server to 2008 R2. SQL server is upgraded to 2008 R2. 

Our web application and specially SSRS reports are build using VS 2005. 

When i click the link to open any SSRS report it pulled the report as expected. 

Most of our SSRS reports have Drill down links to other reports and also open other windows. 

When we click on Drill down link in our website , user gets kicked out of that page to main page. 

At the same time when i access those reports on report server everything works as suppose to be. 

When i host the same website on Server 2003 R2 with IIS 6.5 everything works perfectly. 

I think i am missing some settings or permission which will allow brower to access the report server .

Any help is greatly appreciated.

Manohar