Liferay older versions use JQuery which may be conflicting with your version of JQuery library. Liferay 6 has resolved that issue by introducing AlloyUI which uses YUI library. Liferay 6 does not contain any Jquery library in it so any version you use should go well.
I can think of two ways to solve this problem
- On liferay 5 do not add your own JQuery library. just add the plugin js and see if it works.
- You check the JQuery version which ships with Liferay 5.2.3 and see if your autocomplete plugin works with it.
Hope this helps