In our project we create IIS application pools from code. For this we connect to the metabase with DirectoryEntry. This is COM and the exceptions are ridiculous somewhat cryptic.

Below is code to create an Application Pool. The comments describe the HRESULT of the exception that is most likely to occur on that line of code.

var nameOfAppPool = "MyNewAppPool";
var schemaClassName = "IisApplicationPool";
var newAppPool = default(DirectoryEntry);
var applicationPools = new DirectoryEntry(
    "IIS://localhost/W3SVC/AppPools");
try
{
    // 0x80070005 > no administrative rights
    newAppPool = applicationPools.Children.Find(
        nameOfAppPool, schemaClassName);
}
catch (System.IO.DirectoryNotFoundException)
{
    // 0x8000500F > SchemaClassName is wrong, 
    //              no administrative rights
    newAppPool = applicationPools.Children.Add(
        nameOfAppPool, schemaClassName);
}

// 0x8000500C > unknown propertyvalue
// 0x80070585 > unknown index (= unknown propertyvalue)
newAppPool.Properties["ManagedRuntimeVersion"][0] = "v4.0";
// 1=Classic, 0=Integrated
newAppPool.Properties["ManagedPipelineMode"][0] = "0"; 
newAppPool.CommitChanges();

To use this code in newer versions of IIS check the IIS6 Management Compatibility in the Windows Features.

References

• Metabase Property Reference
• IIS 6 Compatibility components