What I did was install the 2.6 package first on my Joomla 1.5 site (which worked fine, it seems), then I migrated using Jupgrade.
OK, so supposing the article you pointed me to is right and that is indeed the problem I have, should I remove all uddeim tables from my database and then try uddeim 1.6? Is that what you are saying? Since the uddeim component doesn't show on my list of components, I can't uninstall it in the tradition way.