I have several property groups registered and working well. I am now trying to add a few more but the Register property Group button doesn't seem to do anything because when I try to use one of the new entries I get a message saying that property group is not registered. I don't see any mistakes in the xml file so just not sure what steps to take to sort this out.
When you edit the xml data, did you see your definition there?
After register the new xml definition did you click in the register button ? the register button really apply the changes you have done in the xml
Finally, did you enabled the metadata in the profiles ( first tab in the left bottom corner)