I remember trying to troubleshoot this issue but as mentioned we did not find the final cause for it.
Might be worthwhile checking if installation of Service Pack 1 for AutoCAD Civil 3D 2013, which was released last week fixes this?
This problem was solved here by uninstalling Framework 4.5 and installing Framework 4.0.
I am now able to run both 2013 and 2014 version of the Subassebmly composer.
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