Setelah upgrade WordPress muncul error. Ketemu solusinya sebagai berikut :
Problem
After doing the upgrade, and received WordPress upgraded successfully message, but the following message still displays:
An automated WordPress update has failed to complete – please attempt the update again now.

Solution
Delete the .maintenance file found in the WordPress root/base folder, the do the Upgrade again.

http://codex.wordpress.org/Dashboard_Updates_Screen