I've just upgraded a site from D6.26 to D7.16, with views version 7.x-3.5, and if I try to edit an existing view (e.g. frontpage) or create a new view, once I click save I get "The website encountered an unexpected error. Please try again later."
update.php did not report any errors during the upgrade.
Any ideas? (and any way to get better error data?)