That's a good question... Here's where I'm at with this problem:
Following tech support's suggestion, I moved the MM.db from the NAS to a local PC on the network (at first, on my main workstation, later on the HTPC). This works flawlessly on either PCs and the HTPC is far from a powerful machine (Atom 330 1.6ghz, 2gb RAM, 5400rpm drive). The music files are on the NAS, as always. The problem occurs only when the DB file itself is on the NAS. Support's conclusion was that this obviously singled the NAS out as the culprit so that was the end of that... in reality, it's more complicated.
I uninstalled MM completely and rolled back to the latest MM3 build (before they moved to MM4). This works perfectly even with the DB on the NAS. Obviously MM3 is not a viable solution (I wish!) because Tag from Web is broken, but I wanted to test... so it seems the issue is the way MM4 queries the DB has changed since MM3, and that change is negatively impacting relationship with the NAS.
This is really puzzling and frustrating. My problem differs from yours a little bit in that when the DB is on the HTPC (with music files on the NAS) (as opposed to you with the DB on a server still causing problems), I can access the DB from my workstation without lag or any issues. So that's a relative workaround for me, though it requires that the HTPC be always on (which it pretty much is so that's fine). I would greatly like to understand what happened with MM4 so that it's now essentially unusable with the DB on a NAS though!


