Make sure you are running QV11 since the LoadExtensionScripts method was added in that release.
Also it seems you are referencing a sub-folder in your extension called Scripts. Make sure you also have a definition.xml in there.
The definition.xml needs to present in every folder of your extension or atleast in the bottom node of your folder structure. The definition.xml file itself can be pretty empty, no need to define any dimensions or expression but it needs to be there.
Also if your jQuery plugin does not require 1.9 we ship 1.7.1 of jQuery and jQuery UI version 1.8.6.
Atleast you will save some performance on the scripts loading
Copy your definition.xml file to scripts folder