>Sorry, I should have mention it in a first place: this is a WebForms application. As per Christof's I am now using Path.GetTempPath for the HTML file destination which seems to be C:\Windows\Temp on the server. Should I make sure that the IUSR account have access to it?
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If you're running on Windows Server 2003 (IIS6), you'd need to make sure the "Network Service" account has access to the directory where the HTML file will be written. IIS 5 used IUSR/IWAM