December 9, 2015 –
File uploads are failing due to a MS update that affect IIS.
This is a global issue with multi-part form submissions so users of many applications are having problems so I suspect another patch will fix this problem.
Here is the a thread on the Microsoft IIS site about it:
https://forums.iis.net/p/1229356/2114000.aspx?Re+Windows+Update+breaks+multipart+form+data
That patch is
KB3104002
If you can un-install that patch you can resolve the problem.
We will keep you posted.