The main error I’ve seen when using these 2 plugins and using WordPress’ jQuery is “jquery form.product_form .livequery is not a function” which makes it look like the wp-e-commerce plugin is at fault but it actually isn’t. I know it isn’t because I de activated all my plugins and re activated them one by one until the error came back. With my specific set up the error only came back when I had cforms and wp-e-commerce activated at the same time.
The easiest thing to do is FTP into your server, go to wp-content/plugins/cforms/js, open jquery.js and paste in a copy of jQuery 1.4.4. Doing this will not disrupt cformsII on the backend or submitting forms on the frontend.
If you upgrade cforms you’ll have to do this all over again. But since you’re not editing lines of code this is a snap to repeat.
* Note: Just because FireFox Web Developer or Firebug are reporting JS errors doesn’t necessarily mean things are not working as they should be. But you should remember that Internet Explorer is going show a nasty message: “error on page” or “done, but with errors on page” that your clients and their customers will see. But if you fix it before they see it it can be one less thing you’ll have to hear about.
This advice can be used with other combinations of plugins. If any plugin is enqueuing its own copy of jQuery that is not 1.4.4 and you’ve already enqueued WordPress’ jQuery you can just empty the plugin’s jquery.js so that its enqueuing an empty file or paste in 1.4.4. You’ll have to make sure doing this doesn’t stop the plugin from functioning, I’ve only tested this “fix” with cformsII.
In any event as long as everyone is using the same version of jQuery there won’t be any errors.