PDF is generated with error

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IIS6

C#

Java

IIS

IIS7.5

We have recently migrated from IIS 6(Windows Server 2003) to IIS 7.5(Windows Server 2008 R2).

Below functionality of downloading PDF is now giving error: "PDF is is damaged and could not be repaired."

From a public website say, www.abc.com has a link to download a PDF.
While clicking on link, it will redirect on another website say, www.xyz.com(Developed in JAVA) with proper query string.
now from xyz.com it process the query string and connect to another website say, pqr.com(developed in .Net, the migrated one from 3.5 to 4.0 as well as IIS 6.0 to 7.5)
pqr.com actually creates pdf and send to xyz.com and xyz process with headers and it will popup to download.


This was working before but after migration PDF gets downloaded but with the error of damaged file.
Even surprising is when pqr.com/querystrings is invoked,PDF gets downloaded successfully without any error
but, when xyz.com/querystrings (which internally calls pqr.com) is invoked it downloads pdf with error.

Please help on this