Hi mkiwa,

What version of the platform do you have? The HTTPRequestHander is part of the System Components solution, so you should use a more recent version of it. I would recommend you to publish the latest version of the System Compoenents to make sure all of them are the latest versions. Old versions will not work correctly.

As for how to fix the incompatible references. You need to open the eSpace in Service Studio and click on the Refresh References button.
In .Net on recent versions you can also publish the "Current Version" of a solution that will take care of refreshing all references of all eSpaces in that Solution.

Regards,
João Rosado