- Make sure your date and time is set correctly, especially the year.
- Verify that the build you're downloading was built for the correct platform (ie. trying to install an iOS build on an Android phone won't work).
- If installing to an iOS device, make sure the build's provisioning is correct for your device ("Unable to Download..." error).
- Ensure you have enough free space (common on older Android devices).
- Reboot the device.
- Try another device.