Finally found someone today who knows what he is talking about at Paypal.
If you are getting that message and have been unable to use Multi Order Shipping for the last 3 weeks, YOU ARE USING WINDOWS 7 and you have WIndows Update set to "Never check", then I have your fix.
There was a security rollup update KB4012215 for March that fixed some XML security problems. The patch may have been in another prior update, but it was certainly in the Quality Rollup.
If like me you had not done any updates in a year, you might be there a while, but getting up to date with the Important Updates has MOS working properly for me again.
Good luck,
Madkiwi
