I had recently switched AV to Adaware and it seems the Network protection function may have been the culprit. I have turned this off and not had a problem since.
I realise that I have left out a crucial point in my earlier post.
The issue only seems to occur when I am playing media from my Windows Home Server 2011 box. If the media file exists locally on my desktop I do not experience this problem.
I noticed it started a couple of months ago. The only thing I can add to what is above is that it seems OK the week before MS Patch Tuesday. After I install updates the crash/looping problems occur again.