In order to use SQProxy with IIS for a Web site, you have to ensure that SQProxy has the correct permissions to run. Here's how to do that:
Click the Windows Start button, choose Run, enter "%windir%\system32\comexp.msc /32", and click OK to run the Component Services application.
Choose Component Services, Computers, My Computer, DCOM Config.
Find SQProxy.ParameterCollection, right-click it, and choose Properties.
Select the Security tab. Under the Launch and Activation Permission section, select Customize and click Edit.
Click Add, type IUSR, and click Check Names.
Click OK until all dialogs are closed.
Go back and ensure Local Activation and Local Launch are checked.