Loading custom jQuery is the single cause for a huge number of the support tickets I handle. Sometimes developers decide to load jQuery from Google, sometimes they include a version with their plugin files, sometimes they enqueue it semi-properly, and sometimes they don’t even enqueue it. This snippet is an example of all the bad ways to load jQuery in a plugin.
Custom versions of jQuery should never be loaded by plugins. The only exception is a plugin that is built specifically to replace the default version of jQuery.
Not only is this script loading a custom version of jQuery and not enqueueing it, the developer decided to use v1.4.0! This will break just about every single plugin and theme that uses jQuery, especially if the functions being used are only in a newer version of jQuery.
Submitted by Anna Ladoshkina.
If anyone would like a more in-depth explanation of the problems this can cause, ask in the comments and I”ll be happy to elaborate.