Breakpoint will not break in Silverlight
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I am unable to hit a breakpoint on the server side of a Silverlight web application. I know the code executes as I can break on the asynchronous callback with what I was expecting. It's only my machine with this issue.

I am aware this seems to be a common question, however all the answers to the ones I have seen have not helped me, including:

 - The **breakpoint is red** indicating it will be hit.
 - **Silverlight checkbox is checked** on the web project's properties.
 - Clean & build the solution.
 - Getting a new version from source control.
 - Cleared everything from my web browser: cache, cookies etc... (**I am using IE**).
 - Clearing the temp files in %windir%/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files.
 - Checked that all projects are being built in the configuration manager.
 - Everything set to debug and not release in the configuration manager.
 - Manually attaching to the w3wp.exe process.
 - IIS reset.
 - IIS is set to use .NET v4 and the pipeline set to classic not integrated.
 - Reinstalled IIS and freshly configured.
 - Reinstalled Visual Studio.
 - Reinstalled Silverlight.

I am using Visual Studio 2010 (.NET 4), Silverlight 4, and using IIS (I think 6, cannot remember) to host the site.

Interesting behaviour I have discovered (may help to diagnose):

 - It will still not break if I use Visual Studio's own development server to host the site instead of IIS.
 - I saw a blog post (cannot remember where or I would provide a link) under Debug -> Windows -> Proccess (Ctrl D, P) to check that the w3wp.exe process is set to "Silverlight" under the "Debugging" header - mine was set to "Managed" and was unable to set it to silverlight when attaching. After checking a colleagues settings on a machine which was working, his was also set to managed.

Any suggestions will be very appreciated! 