Manage Plugin updates doesn’t seem to be working

I’m using WordPress 2.8.6. There seems to be a problem with the Manage Plugins page. It says a plugin needs updating but the plugin isn’t getting updated. I click on the “update automatically” link and get a series of messages that it is doing its thing and did it successfully but it really didn’t. The plugin is still at the old version and the Manage Plugins page still says it needs to be updated to the newer version. I’ve tried this several times even logged off and shut the browser down to try again–still doesn’t work. For example, TFS Core (Text Filter Suite) and TFS Acronymit are at version 1.0. The update is supposed to be for version 1.1.