Would importing two versions of jQuery cause plugins to stop working?

Would importing two versions of jQuery cause plugins to stop working?

Hi folks.  I'm brand new to jQuery, so I apologize if this is a 101 question, but I'm trying to sort out a production issue.

I do QA for an ecommerce website.  When one of our developers made some changes to our application recently, a couple of the plugins we use stopped working on those pages.  Looking at the code, it seems we load jQuery 1.4 and several plugins, including autocomplete and popdown.  In the changes, for some reason, the developer loads jQuery 1.4.2 (after 1.4 has been called) but doesn't call the plugins again.  I'm assuming that this is the reason the plugins stop working.  Can anyone confirm this theory?

(The reasons why we don't call 1.4.2 earlier in the document are, sadly, mostly bureaucratic.  If I can get this confirmation, hopefully I can push through that.)

Thanks very much!

Joe Helfrich