picasaView enables you to view your picasaweb-albums in your blog - simply by specifing a tag in your content.
That means either your connection settings are wrong (i.e. wrong picasa-url or wrong picasa user-id) or the plugin can't connect to picasaweb. The failure message from picasaweb should appear below. If you have problems troubleshooting, don't hesitate to contact me (along with as many infos as possible, like your config settings, WordPress- and PHP-Version and so on).
This means that neither a custom template nor the default templates were found or not readable. If you use custom templates please ensure they are placed in 'WP_DIR/wp_content/picasaview_templates' and have the same name like in the default templates dir in the picasaView-plugin directory.
If you're really sure your data is correct, ensure that the albums of your picasaweb-user are made public or you specified an authkey for private albums.
Be sure to use the shorted album name picasaweb generates, not the original one. For example the album "Cats And Dogs" is shrinked to "CatsAndDogs". You can see the shortened album name if you click on an album in picasaweb and look at the url: "http://picasaweb.google.com/username/CatsAndDogs".