Problems with Widget manager

Hello guys, this time, I come with another problem. I install widget manager in elgg 2.1.2 and I got many errors, I mean, after I activate the plugin, when I clic on a menu with submenus it don’t expand, the same thing happens when I try to add widgets to my profile. I’m not sure of what is the importance of the plugin but it is recommended but many other plugin so I installed it. I hope you can help me. Sorry bad English.