Francisco Guerreiro,
Are you getting following screen when you are trying to drag and drop items?
If yes
a) have you updated all of your plugins?
Update all plugins. If updates for some plugins are not available yet, deactivate them one by one. One of them might be causing this issue.
b) have you updated your theme?
What do you mean by "remove mobile platform"?
You will need to restore your site from back up to downgrade to 1.5.
If you just don't want your users to be redirected to mobile version check this topic:
http://www.oxwall.org/forum/topic/15550