Every time I want to save / save & close / close a product in Virtuemart 3, this error appears in my console; and obviously, buttons don't work... what is it? how can I fix it? http://gyazo.com/b4662b8b36c5f76d3dea95559e08c4df
VirtueMart is just recently migrated to Joomla 3. It is not fully comatible with a pure JQuery environment.
Please, check this tip to force Mootools compatibility in legacy code:
Mootools on Joomla 3.4 - Fix to broken extensions https://groups.google.com/forum/#!msg/joomla-dev-general/pJ8gi8LypuE/Lsgryh77ClgJ