You may be experiencing any of these problems:

• Errors when trying to send picture messages (MMS)
• Errors when trying to access data or the internet

This issue can usualy be resolved by checking mobile network settings and resetting the APN (Access Point Names). Some battery saver apps disable the APNs or data connection when the battery level gets low. You can uninstall the app, or follow these steps to adjust APN and data connection settings:

1. At the Home screen, tap the MENU button.
2. Navigate to Settings > Wireless & networks.
   NOTE: This path varies on different software versions.
3. Verify that the Airplane Mode or Flight Mode check box are cleared.
4. If you see a Mobile Network check box, verify it is selected.
5. Tap Mobile Networks.
6. If you see the following check boxes, verify they are selected:
   
   Data Enabled
   Use Packet Data
   Data Roaming
   
   
7. Tap Access Point Names or APNs.
8. Press the MENU button.
9. Tap Reset to default.
10. Press the HOME button.
11. Test your data connection by accessing a web page or sending a picture message (MMS).

NOTE: If the issue continues, verify the APN settings with your service provider.