In Visual Studio 2008 (or 2005), Right-click in the IDE's toolbox and click Choose…. Locate the HCCust assembly inside the Bin\Release folder, then add it to your toolbox. You'll see a new item called a "HCDropdownlist". Use it like a normal dropdown (it has no additional properties or methods, but won't give the invalid callback problem) in Ajax mentioned in my blog posting.
Placed into the public domain by its creator, Atomic Avenue, Inc. Use it in good health for whatever you like with no restriction.