There is a thread over on We Got Served talking about people experiencing stutter on blu-rays when demigrator.exe or other write intensive applications write to the WHS disks.  In my case, this usually happens once or twice per movie for anywhere from 30 seconds to a few minutes, but it never happens with DVDs.  Reading data doesn't seem to affect playback at all, but writes screw it up almost every time.  My blu-rays are stored as ISOs on WHS and stream to my 7MC machine using Virtual Clone Drive and Arcsoft Total Media Theater.  If I disable the Drive Extender Migrator process, my blu-rays play perfectly every time.  If you are having the same problem, please log it on Microsoft Connect here:

https://connect.microsoft.com/WindowsHomeServer/feedback/ViewFeedback.aspx?FeedbackID=515270&wa=wsignin1.0

Also, the original thread is located here:

http://forum.wegotserved.com/index.php?/topic/8335-demigrator-exe-again/page__pid__51418__st__0&#entry51418

Our hope is that everyone who experiences this problem will log it and Microsoft will fix the issue.

Wow. I have been suffering with this for so long, and have searched elsewhere, but never knew about Demigrator. Thanks for the links. I can't believe MS hasn't fixed this, given how long that thread has gone on for. I can't say how many hundreds of hours I've wasted trying to find the solution to this problem, diagnosing my network, installing new software, reinstalling, rebooting, etc, etc. Here's hoping this also fixes HD TV recording stutters, another problem I've had for so long. So much so that my family would rather watch SD content than deal with the HD issues.

Because it will probably get lost in the origional thread, and because it has caused me almost as much pain as it seems to have caused you... here's a link to the work around I am using that has eliminated the problem for me - http://forum.wegotserved.com/index.php?/topic/8335-demigrator-exe-again/page__st__180__p__73857&#entry73857