Get user account

How do I get the executing assemblies user account?  e.g.  ASPNET, IUSR, IWAM, etc

 My site calls a DLL that has some logging built in and works with it's own console test app, but does not work when referenced by my web app.  I'm trying to determine if it's a rights issue in that it can't get access to write to the log file.  I'm not sure what account it being executed under.

  

Thanks,

Sean
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