System.OutOfMemory exception the second time a page is run

We've got a web app that takes XML and transforms it to HTML using XSLT, then renders it as an excel download. The problem is, the XML is so large that the second time the report is run, the XML creating throws a System.OutofMemory exception. If I restart IIS or wait about 10 minutes (garbage collection), it doesn't happen, but the users can't run subsequent reports.

 We tried calling the garbage collector.Collect() method, as well as using the Using keyword, to no avail. The objects taht are taking up all the memory are a string and a memory stream.

 Does anyone have any ideas on what we can do to rectify this?

 

Thanks,
Chris
...