BUG: "ExternalException: Cannot Execute a Program" Error Message When You Call WebServices from .aspx Page

If you use Simple Object Access Protocol (SOAP) to call the WebServices method from an .aspx page, the .aspx page may fail when you run the Microsoft Internet Information Services (IIS) Lockdown tool. In addition, you may receive the following error message: This problem only affects Web applications or Web services that are clients of a Web service and that impersonate the Anonymous user account.

The IIS Lockdown tool denies execution access for the IUSR_COMPUTERNAME and the IWAM_COMPUTERNAME accounts to every executable file (*.exe) in the Windows directory (%windir%). This includes framework tools such as the Csc.exe file, which the XmlSerializer class uses. When a Web application or a Web service impersonates IUSR_COMPUTERNAME or IWAM_COMPUTERNAME, the Web application or the Web service cannot use XmlSerializer to serialize objects into Extensible Markup Language (XML) documents.

Note This problem does not affect the server side of a Web service because XmlSerializer is generated and compiled outside of the impersonation.

To resolve this problem, use one of the following methods:

• Use a different, non-Anonymous account to impersonate. (This is the recommended method.)
• Add sufficient permission for the executable files in the Windows directory.

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

Steps to Reproduce the Behavior

1. Allow Anonymous access on the IIS application.
2. Enable impersonation for the Web application in the local Web.config file as follows:

   <configuration>
     <system.web>	
   	<identity impersonate="true" />
     </system.web>
   </configuration>
   					

3. Run the IIS Lockdown tool, or deny access to the IUSR_COMPUTERNAME or the IWAM_COMPUTERNAME account on the Csc.exe file before you request the page.

For additional information about impersonation in an ASP.NET application, click the following article number to view the article in the Microsoft Knowledge Base: For additional information about XmlSerializer, click the article number below to view the article in the Microsoft Knowledge Base: For more information about Web services, refer to the following MSDN Web sites: In addition, refer to the "Creating and Accessing Web Services Walkthroughs" topic in the Visual Studio .NET Online Help documentation for more information about Web services.