Got this obscure error while calling a web service method that requires a Xml serializer:

“Unable to generate a temporary class (result=1).\r\nerror CS2001: Source file ‘C:\\Windows\\TEMP\\qdrb02m1.0.cs’ could not be found\r\nerror CS2008: No inputs specified\r\n”}  System.Exception {System.InvalidOperationException} “

 

Web searches on key phrase “Unable to generate a temporary class (result=1)” returned some useful results but none could directly resolve my issue. But general direction was pointing to the proper permission of the ASP.Net surrogate identity that most likely does not have sufficient right to the local I/O where XML serialization takes place.

To prove this, I fired up a console application and called the same web service method; as anticipated, the Console app did not throw error at all. So that’s true – it is to do with the Windows account that IIS uses to run the ASP.Net process.

By default, IIS7 uses “ApplicationPoolIdentity” as the Identity for the Application pool automatically created when a new website is added to the IIS/Sites. But what’s underneath this mysterious “ApplicationPoolIdentity” – you could not even find it in Windows by looking up user accounts? Below are several things I tried and let’s see how they fared:

1. I tried to give “Full Control” permission to ASP.NET Machine Account on c:\windows\Temp folder. Not work.
2. Changed the app pool identity to “Network Service” (via IIS7/Site/Advanced Settings) and gave the “Network Service” full control permission to c:\windows\temp (via Windows Explorer). It worked! Then I reduced permission to only “Read, List Folder Contents”, and it still worked.
3. Changed the app pool identity to “Local System”, of course that worked too.

 

So, at the end, to get rid of error “Unable to generate a temporary class (result=1)..”,  I ended up using the “Network Service” as the Application Pool identity (leave the security mode as Integrated) and granted the “Network Service” account permission “Read, List folder contents” on “C:\Windows\Temp” folder.

P.S.: after I deployed the web app to my staging web server, the error returned. The staging server is running IIS6 and the app pool identity by default was already tied to “Network Service” account. So I went directly to the c:\windows\temp folder and as I anticipated, the account did not have “read, list folder contents” permission. So I granted the permission to “Network Service” account and then it all worked!