Vlk et al, sorry to say, I'm now having the same issues - on all network computers. Can confirm description and remedial action taken by trebmal - replicated actions and same results, EXCEPT that after reboot, my networked computers are still active (no need to restart service). I'll watch it and keep working for the next few hours but, in hindsight, I started hitting the first signs of network problems earlier this afternoon, about 4-5 hours after we did that work with wftest this morning (initially, I thought the gradually worsening problem was something else).
Will post back later as required. Hope you can come up with something.
20 mins later: Vlk et al, the problems I started having earlier this afternoon began when I was doing some tagging on the media library held on WHS. started doing more of this work a few minutes ago and the same problems re-emerged immediatly. A few minutes prior I'd been working on a shared document in another shared folder and that seemed fine. So at this stage, I'd say it's associated with media sharing (for your info: my primary media software is J River Media Centre but I've just closed and cranked up WMP to find the same issues). As things stand right now, my system is in the same state described earlier by trebmal and confirmed by me. I'll keep messing for a little longer (although I'm not sure what to mess with, to be honest) but I'm very close to having to uninstall Avast WHS from the server (perhaps I'll reinstall the Server Edition trial - I still have a week, I think, on my trial version) - I've lost complete functionality with shared folders so I can't do much else if I'm to keep working - which means, of course, I won't be much help to you... sorry...
10 mins later... no, hang on. When the system goes into this state, according to connector on the client, things are still fine - full communication and no reports of anything 'unhealthy' (I know that nothing's being 'damaged' on WHS - it's a communication issue). However, as described, can't open 'shared folders' on the client via usual means - in fact, SERVER (shared folders) doesn't even show in Explorer (times out, 'no privileges'). But the interesting bit is, if I then go to the server and log on (I'm running it with a monitor and will for several months yet), I can't even access the Shared Folders from the server desktop - no response and then it freezes. Even Task Manager won't make it end process, return to nornal. Only way to get server going again is to reset/reboot. Some kind of incompatibility between Avast for WHS and shared folders occurring on the server itself - perhaps triggered by particular actions on the client? And, of course, since the server has been rebooted, I now have full access again on the client.
I'll keep grinding away on the client and try using items in the shared folders that ARE NOT media and see if it generates the same effect. (BTW: printer and file sharing functioning fine).