A lot of time can pass between the moment a stack trace is generated and the moment the stack trace is thoroughly investigated. During that time, a lot can happen to the file in question, sometimes obscuring the original error. The error might have been fixed in the meantime (overlapping bugs).
Is it possible to get Stacktraces that show the offending file at the time of the error?
Not elegantly, and you normally don't want the user browsing through code that's throwing unexpected exceptions anyway (open door to an attacker).
Usually, what happens in a dev shop is that the user reports an error, stack trace, and the build it occurred on. As a tester, you can grab that build from your archives (you ARE keeping an archive of all supported releases somewhere handy, RIGHT?), install, run, and try to reproduce the error, working with the user to provide additional info as necessary. I've seen very few bugs that couldn't be reproduced EVENTUALLY, even if it required running the program against a backup of the user's production database to do it.
As a developer, you can download that build's source code from your version control repository (you ARE using version control, RIGHT?), and examine the lines in the stack trace to try to discover the problem by inspection, and/or build and run it to reproduce the error. Then, you go back to the latest source version, build, and run the same steps (a UI automation system can help out here), and if you don't get the error, someone else already found and fixed it. If you still get the error, you also got an updated stack trace with lines that match the current build, allowing you to set your breakpoints and step through.
What KeithS said, plus there are ways to capture more helpful state information at the time of the Exception using the Exception.Data property. See http://blog.abodit.com/2010/03/using-exception-data-to-add-additional-information-to-an-exception/
While KeithS' answer as pretty much correct, it can be easier and more elegant than you think. If you can collect a dumpfile (instead of just a stack trace), you can use a Symbol Server and Source Server in combination with your debugger to automatically pull your correct-version code from source control.
For example: if you enable PDB output and source-server integration in MSBuild, and upload the resulting PDBs to a symbol server, Visual Studio can automatically load the correct source control from a TFS or SourceSafe repository based on the information in a minidump.