Hi ludirois
and welcome to our forum
There is a button on top right in jOpenSim map administration called "map settings". All values (except the first and last 2) are to be entered in pixels. So if the "grid map width" and the "grid map height" are 0, your map probably is there but has 0 pixel width and height.
Value no.4 to no.6 should actually read "region" instead of "map". This typo will be corrected in the next release again
But if you mouseOver on each label, it should give you more hint, what the value means.
Greetz
FoTo50