A .svc WCF service doesn't work in ASP.NET on IIS 7.0-8.5

I've added a .svc file to my Web Project - it won't run. When I request it (it's hosted in IIS manually) I get. How ever when I run the Web Project in the Azure Emulator it DOES give a valid response (the overview of the service).

The error:

The filename, directory name, or volume label syntax is incorrect. (Exception from HRESULT: 0x8007007B)

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

[FileNotFoundException: The filename, directory name, or volume label syntax is incorrect. (Exception from HRESULT: 0x8007007B)]
   System.Runtime.AsyncResult.End(IAsyncResult result) +622882
   System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result) +196075
   System.Web.AsyncEventExecutionStep.OnAsyncEventCompletion(IAsyncResult ar) +166

Never really found the cause, but changing around some application pools made it work.