With keyboard mapping MESS defaults to a direct physical mapping. For PCs that means keys pressed are translated into "what's there on a US QWERTY keyboard" in most cases, so if you're running a non-QWERTY layout or non-English OS hilarity may ensue. Turning on "natural keyboard" mode usually helps that - it changes the mapping to "what's actually printed on your keyboard".
When I say "completely up the spout" I mean it's completely
up the spout. It's not a mapping issue, it's sort of... Press "F" and watch it type "]1<new line>" or something daft.
It does boot though....