Question: In our TFS server 2013 we have several projects  

(Eg : P1, P2, **P3**, P4)

When i'm going to **check in** the codes to a single project **Eg : P3** i'm getting below listed errors in output window of visual studio 2013.
(but team connecting and other source control functions are working fine)

> 
> All of the changes were either unmodified files or locks. The changes have been undone by the server.
> 
> 
> Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host.
> 
> 
> The server returned content type text/html, which is not supported.
> 
> 
> TF30063: You are not authorized to access
> 
> 
> 

[![output window of visual studio 2013](https://i.stack.imgur.com/5WfwR.jpg)](https://i.stack.imgur.com/5WfwR.jpg)

also some time it was working and I will get this message

* Changeset 1874 successfully checked in

Other projects are working fine Eg: P1, P2, P4

Answer: 
It looks like something is intercepting the call and blocking it. TFS would normally always return a reponse type of `soap+xml`, `xml` or `json`, the fact you're seeing `text/html` indicates that a HTML error page is presented for some reason.

I suspect it's your Virus scanner locally (if it provides web traffic protection), or an upstream proxy server or the anti-virus on the TFS server itself. That or your TFS server itself is really running into trouble in which case the eventlog on the TFS server should have a ASP.NET crash report.

The easiest way to troubleshoot this is to install and run fiddler and try the check-in again. Look up the response you're getting and look at the HTML message. I suspect it will hold the actual error message and it will likely tell you the exact source of the error.

---

As you reported, it was SonicWALL which is blocking the request before it reaches TFS. So either there is something fishy with the contents of the NuGet package, or the SonicWALL rules need to be adjusted to accept certain traffic to your TFS server.
As per @jessehouwing I used the fiddler and figured out that below file was blocking by the SonicWALL Gateway Antivirus Service.

**<http://.../tfs/.../VersionControl/v1.0/upload.ashx>**

**<http://.../tfs>**

[![enter image description here](https://i.stack.imgur.com/EIgwg.jpg)](https://i.stack.imgur.com/EIgwg.jpg)

and all TFS paths are allowed from firewall and now its working perfectly.