POSTing data to WebApi after update to 5.1.0 fails

I found the problem.

My post code uses $.ajax(...), as shown in initial message.

But jquery's .ajax post data as application/x-www-form-urlencoded.This worked in previous versions of WebAPI, but in latest update it seems it doesn't accept application/x-www-form-urlencoded by default.

I changed content type to application/json, and I had to convert data to json, and this solved the problem.

So, instead of

j$.ajax({    type: "POST",    url: uri,    data: dataObj,    success: function(...)

I had to change to

j$.ajax({    type: "POST",    url: uri,    data: JSON.stringify(dataObj),    contentType: "application/json; charset=utf-8",    success: function(...)

First clue:

Removing enableCrossAppRedirects="true" from Authentication settings of web.config resolved the issue in my case. Thanks to @kiran-challa

Ok, I found the fix for this without a work around.

Refer to this thread:h t t p : / / a s p n e t w e b s t a c k . c o d e p l e x . c o m/discussions/524616

This is a bug in 5.1 - it is resolved in a nightly buildSee: https://aspnetwebstack.codeplex.com/and specifically Signed nightly builds:

"Nightly builds can be used with Visual Studio 2010 SP1 or Visual Studio 2012. To use the nightly build:1.In your Package Manager settings add the following package source: ....
2.Add or update to the latest build of ASP.NET. The nightly build is labeled (nightly YYYY MMM DD). "

this fixed the post issues for me (no need to use JSON.stringify anymore) and also fixed multi-part posting for a module that was uploading a file.

Hope this helps someone else!And hopefully there will be a proper patch for this soon.