Certificate issue App Store
Cannot launch App Store from iPad ....notice of certificate error. Help!
iPad 2, iOS 6.1.2
Try a reset: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps from the tray before doing the reset.