I've had problem, where I named a level with a dot/period (.) in the name, as in "start town v.2". And then when I tried to open up the level again nothing happened, it would not open the level even though you could see it in the folder. Then I manually changed the name in the file, editing out the dot, and then it would open the level again, albeit it got bugged.
So what I deduce is "don't use dots in the name of a level".