Configuration :: .net App That Calls An Exe Under Alternate User Context?

I'm banging my head against a wall here... can't get to the bottom of this issue. I have code that works fine when debugging in visual studio but breaks when deployed to both IIS 6 and IIS 7.5. Basically, it uses Process and ProcessStartInfo to start a program
(a command line tool, exe) and redirect the output to the web page. It uses the username and password properties of the ProcessStartInfo class to run the exe tool as a specific user. The tool requires admin privelages so I need to run it as such, but certianly don't want to run the IIS service or the asp.net app pool under an admin context.

No exception occurs when run on IIS, but it does not work, when trying to run on IIS 6 I get this error dialog: "The application failed to initialize properly (0xc0000142). Click on ok to terminate the application." It's obviously a security/config issue, but what specifically is the culprit? For IIS 6, an application pool was created for this, runs under 'network service', as usual, but again the process being started by the system.diagnostics.process class is run under a different account, which is an administrator account. For IIS 7.5, same thing,an app pool was created, so it runs under the 'iis appPoolNameOfPool' context.