Seeing as I'm in an editing state-of-mind at the moment I thought I'd share ten of the best errors I've found during recent or previous editing of my own manuscripts (GPL, MMA or other works-in-progress). They are in no particular order, although my favourite is unquestionably number 10 (mainly because I found it two nights ago).
1) Non POV character's facial expressions are described even though characters are in a pitch-dark room.
2) Characters don't eat for four days but never complain of hunger.
3) A horse gallops for eight hours.
4) Characters don't sleep for two days but never complain of tiredness.
5) The Moon is full twice in a week.
6) An 80 mile journey is carried out in two days (on foot).
7) A major injury is forgotten the next day.
8) Fires are lit effortlessly without tools/implements/matches.
9) The Sun sets in the East.
10) A character uses an axe to chop the leg off a table so the table-leg can be used to try and break through a rusted iron bar (this one might require a moment's thought).
All I can say is how glad I am I caught these!