When you upgrade to a new version of WordPress sometimes the procedure “forgets” to clean up the stuff downloaded to perform the update. Sometimes, this depends on various factors (wordpress version, hosting, etc.), the upgrade is successful but a message appears on your dashboard: “An automated WordPress update has failed to complete”, though a bit more below it says you are using the updated version of wordpress. I usually solve this situation by:

• deleting the upgrade folder into ./wp-content
• deleting the .maintenance file into the wordpress root.

The second step might be a bit tricky for non-expert. You need an ftp client which allows visualizing hidden files (those beginning with a dot). Then you can select it and delete it.

If you solve this issue in a different way I’m glad to hear your opinion in the comments below.