Like all devices, even the Nintendo 3DS succumbs to errors. This past weekend, a number of 3DS units have displayed a black screen due to an error. 

The black screen of death, a pun of the Xbox 360's red ring of death, has plagued a number of people whom received the error notification whilst playing their brand new 3DS. The message reads as follows:

An error has occurred. Hold down the POWER button to turn off the power, then turn it on and try again. If the problem persists, please contact your local customer support center.

Those that experienced this annoyance have been able to do a hard reboot of the system by holding down the power button for a short time. Some others haven't been so lucky and have brought back the handheld to the store and replaced it.

Formatting the SD card of the Nintendo 3DS to FAT32 also seems to be a working solution for some as well.

It appears not setting up your wireless connections properly could result in this error. If the 3DS's wireless switch is set to "on", it will keep searching for a connection and for some, cause this error. This has not been confirmed, but rumored though.

It's important to point out that no hardware is ever foulproof and errors can always happen. If they happen, they'll end up on the internet very fast (case in point) which usually makes it sound this problem is widespread. Thusfar it's been only a few cases and knowing Nintendo the issue will be resolved swiftly or easily.

Source