Recently while working on a project  I encountered an issue with MTM not able to associate with automation.

Association of test case to automation is well explained in this article : http://msdn.microsoft.com/en-us/library/dd380741.aspx

I couldn't associate automation because :

1)  I didnt see ellipses (...) at all in MTM ( under 'Associated Automation' tab ). 

~ So I moved to Visual studio and ran my query to open test cases. I could see ellipse button under 'Associated Automation'.

2) On click it just brings a blank modal window. I do not see any tests in "Choose Test" window".

~ I have a solution opened from TFS.

~ I was able to successfully build them and have the dlls created.

~ But, when I clicked the ellipses (...) in the Associate Automation, I don't see any tests.

Well reason for such behaviour is : Project that I created was NOT test Project type. I created a class library project while i was re-factoring my code.

Simple fix for this problem is make this project as test type or manually modify <ProjectTypeGuids></ProjectTypeGuids>  to 

 <ProjectTypeGuids>{3AC096D0-A1C2-E12C-1390-A8335801FDAB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>