Corrected the comma for the semi-colon, was a typo in the post.
The relative paths in swpath worked until 270, is in 271 when are crashing.
Actually setting paths via mameui gui also crashes the emu too, so will try in another computer if the behaviour is the same..
Edit: Tried in another computer with fresh install. The swpath is completely broken.
Anyway don't mind, I'll use the command line.