I have made the same test and it works for me.
Wich version of Jooma are you using ? (shouldn't change anything, but in case...)
Are you using ajax combos ?
Before to download again, try it on the sandbox.
It works for me on an existing project.
Try new download on new fresh joomla install, and then tell me in wich case you have this error.
Also is this error raising only in modal box ?
If you have JS loading errors, you can upgrade with the last release. This morning I have changed something in dom/dom.php
There was a problem for url treatement (convert path to URL for the assets).
Hope it helps.