WCF, Sitecore, JSON and .NET 4.0 vs. .NET 4.5.1

I have been having an interresting problem the last few days, that took quite a while to debug.

This doesn't only relate to Sitecore, since every WCF service created in .NET that is consumed be javascript can run into this issue.

A little while ago, we upgraded our development machines to Windows 8.1, which includes .NET 4.5.1 - which seems to make some small, but important changes to WCF.

It turns out, that Microsoft has changed how objects gets wrapped, when they are outputted as JSON.

In .NET 4.0, it seems like objects was getting wrapped in an element called "d" - this has been removed in .NET 4.5.1 (it's gone on our machines at least).

The server the website is running on, only had .NET 4.0 installed, so we got permission to upgrade it to .NET 4.5.1 , which after a little too long spinning at "Preparing to configure updates" in Windows Update, we had the server up and running with .NET 4.5.1, which fixed the problem, so the JSON nolonger is wrapped in the "d" element.