In necromancer's lair, dont beak those crates, but stand on them instead ...
For some unknown reason, game believes that many things are far higher then they actualy are ... you can also notice, that this apply for jumpable edges too (especialy anoying in Hag's lair) ... and when you finaly find that place you can jump on, your character will simply jump under that place. o_O
If my comments bother you, there is nothing easier than telling me to stop.
I mean ... I won't ... but it's easy to say.