I have a somewhat similar problem, and I've been following this thread and troubleshooting on my own. I often get the "something went wrong with playback" in theater view mysteriously, often after leaving my computer unattended for a while. I tried to run it down, and I'm not sure if you're seeing the same problem I am (we have different tuner devices), but In my case it seems to be a consequence of JRiver not releasing the TV tuner correctly after long recordings or extended viewing. Let me go over my observations:
I have an HDHomerun Prime, which is an ethernet cablecard tuner with three tuners in it. I can tell when a tuner is active because each tuner has a green light that illuminates when it's active. So here's what I've observed:
1) I only record two television programs in all. They are half an hour each and run back to back on the same channel on weeknights. My server is configured to record the two half-hour programs (one from 11 to 11:30 the other from 11:30 to 12:00). The server successfully records both programs, but when the second program finishes, the tuner light does not usually turn off, even after many hours. After such a recording, when I attempt to watch TV on the client I get either a "something went wrong with playback" in theater view or a "no tuner is available" error in standard view, notwithstanding the fact that there are two other tuners available and not in use. The server, if left alone, will not release the tuner in question (I waited over a day once), but, sometimes, remotely logging into the server, opening up the TV menu and clicking "watch" and then "stop" will release the tuner so that the light turns off and client playback works correctly. Sometimes that doesn't work and the server instance of MC needs to be restarted to release the tuner.
2) Similarly, if I watch TV for a long while on a client PC and then hit stop, the client will sometimes similarly not release a tuner (it will stay illuminated). Sometimes attempting to watch the same channel again on the client and hitting stop again will cause it to release, but sometimes not and then I get the same errors as in 1), and MC needs to be restarted. It seems most likely to get "stuck" after continuous viewing for longer than the time-shift window (in my case longer than 1 hour).
So in my case the error seems to be caused by a computer attempting to use a "busy" tuner and not falling back to the other unused tuners. I confirmed this was the case by changing my tuner settings in the TV options menu, where it lets you choose which order JRiver will poll tuners in. If I set my server and clients to prefer the same tuners in the same order, I get the behavior described in 1) and 2). If I instead set the server to "prefer" a different tuner than my clients, the client still works in case number 1). This suggests that in addition to not relinquishing the tuner correctly that the tuner fallback isn't working as expected in this specific case (i.e. the non-busy tuners are accessible if you explciitly select them, but JRiver doesn't successfully go down the preference list when the first tuner is "locked").
I should add that the fallback behavior works correctly for me in other cases, i.e. attempts to record multiple simultaneous programs works fine, and attempting to watch TV on a client while the server is recording successfully "falls back" to an open tuner as long as I'm doing it while the server is actually recording and not "hung" post recording.
xtacbyme, if your tuner device has multiple tuners, you might want to try setting your client to use a different preference order than your server and see if that results in any change in behavior. It may not help, but it made my system much more usable.
Hope this helps.