Just got to this episode and also having the problem. Currently about 9 minutes into the episode and then displays the message 'Sorry, something went wrong. Please try again later, or head to our Help site to get in touch'. Tried restarting multiple times but it plays for a few seconds and then displays the error again.
Tried restarting the Now TV box (model 4200SK) but the same problem. Connected via ethernet and broadband connection is otherwise fine.
Was eventually able to work around it by immediately rewinding (to about 7 minutes) after starting it playing again and then letting it play through again.
Also, just to point out that Season 4 Episode 4 seems to have some sort of encoding issue as the frame rate is glitching every second or so. It's more aparent on panning shots but is visible throughout the whole episode.
We have also encountered the same problem.
Dexter Season 4 Episode 6 at about 9 mins, wants to skip forward to episode 7 then says: Sorry, there was an error in the player
Have been unable to find a work-around so far.