i have a problem with my mac. when i want to upgrade to OS X 10.10.3

it says "OS X Update could not be verified. It may have been corrupted or tampered...". i tried download OS X update from support.apple.com/downloads. after installing, it just a normal reboot. my mac still in OS X 10.10.2. and then i download OS X installer from Mac App Store. when i want to install it, it says same. could not be verified. my time in my mac is automatically set by apple server. how can i fix this?