What type of trouble is caused? All of a sudden my screen has a line of pixels missing.

Without seeing the issue no one here can tell. Take the laptop to Apple or an Apple Authorized Service Provider to be examined.

Some of the other respected contributors on these forums mention Apple doesn't charge you for examining the computer at the Apple Store. If the computer is under warranty, then an independent AASP probably won't charge you either. You can always ask them before taking the computer.