MERCHANT STAGING SERVER IS UNAVAILABLE

Ran into this with Merchant Warehouse. Was cause by an old version of XP, pre SP3. The XML6 was not in the system32 folder. Get them on SP3 or download the XML6

http://www.microsoft.com/en-us/download/details.aspx?id=3988

I got this issue when a typo is in the merch key. Also got it when not going into WS prefs and saving