DC Universe Online error 0x0121

Restart your device if you haven't already done so. A simple restart can solve a lot of problems.

1. Turn off the device completely by pressing and holding the power button.
2. If your device is connected with a power cable, unplug the power cable from the device for at least 1 minute once you've turned off the device.
3. Plug the power cable back in and turn the device back on.

The error could be related to an underlying network connectivity issue, so it's a good idea to restart your modem and router.

1. Unplug your modem (and your router, if it's a separate device) from power for about 30 seconds.
2. Plug the modem back into the power outlet first and wait 1-2 minutes before turning on the router. Wait for all of the panel lights on your modem to turn green.

Clear the app's app cache and app data to remove any temporary data and files that may cause issues while using the app.

Reinstall the app to remove all data and clear the app's settings.

If you're playing this game or app on a PC, make sure you have the latest graphics card drivers installed, otherwise your games and apps may crash. Depending on your operating system and graphics card, install the latest drivers for your video card.

Turn off DirectX 12 or change from DirectX 12 to DirectX 11 in the video settings of the game you're trying to play. The differences between DirectX 11 and DirectX 12 are quite significant. DirectX 11 provides a much smoother framerate for low-to-midrange PCs.

The Nvidia Geforce Experience overlay can cause video issues and errors while playing games or watching videos. Turn off the in-game overlay.

1. Open GeForce Experience and login if you're not logged in yet.
2. Click the Settings (icon) at the top right.
3. Click the General tab, turn off IN-GAME OVERLAY, and close the program.