For anyone else who is struggling with this ... some extra info. I had almost the EXACT same problem as above - The solution:
Go to your /public_html/wp-content/plugins/ folder (or whatever path you have to your blog) on your web site either via an FTP client (or using your CPanel file manager or any other means of FTP) and DELETE the plugin folder containing the file/s that are causing the error. So for "plugin installer" (as I had a problem with) delete that folder. Similarly for the wordpress-automatic-upgrade shown above (I also had this one from a previous instal/upgrade) delete that folder too.
When you click the plugins link again WP will show some errors showing that the offending plugins have been deactivated due to an error (which is what you want). Bottom line is that there appear to be conflicts between the two plugins above (specifically) and the new embedded "upgrade" facilities within 2.7 so you don't need the plugins anyway.
Can someone with relevant access take an action to add these to the "Conflicting Plugins" list or the "Do NOT work" list please?
Hope the above helps - should also hold true for any other plugins causing problems.
Best regards, Bob Lewis.