Calls to web service get stuck after first request

Few days ago we came across a very strange behavior - our application that connect to a web service go stuck after few requests.

When we ran the application on the server (connect locally) and it worked but from client desktop it didn't.

We suspected something about firewall so we ran wireshark and saw that the the request was sent with Expect: 100-continue header which means that the server getting the request should respond with 100-continue and than the client should send the data in the body

We almost gave up and then one of colleges at work suggested to contact our IT and amazingly that did the trick - apparently they set new firewall in the LAB causing specific kind of request/response to be blocked!