I'm not sure what the symbol could be. As I said, looking at the images contained within the firmware I can't see any that match your description.
My best guess (and it is only a guess) at why the recording failed after 3 minutes is that you tried to record a programme from a channel like ITV3+1 that goes off-air at midnight +/- a few minutes. ITV shouldn't list programmes in the EPG that are not shown in full, but often do. If you set a recording for, let us say, "Lewis" that is scheduled to start at midnight on ITV3+1 and the channel goes off-air at 00:03 (replaced with an off-air caption on the "live" channel, but is unrecordable), this could explain what happened.