Get the following message: Internal Expression Error:'Runtime Error (at 98:835):'=/059' is not a valid interger value. I have now idea what that means.
You have a syntax error in your scenery.cfg, probably around a line which contains a 059. The installer doesn't risk touching an already corrupted scenery.cfg, because it might risk corrupting it even more.
There are already many cases of corruption that are gracefully handled by the installer, so it can at least issue a clear error message but, perhaps this one wasn't expected, so the error is more obscure.
It would be really helpful if you would Attach (or send me via email) your scenery.cfg, it would help improving the installer handling another case of scenery.cfg corruption.