This error is specific to older Android versions (including but not limited to 4.4.2). The root certificate on the device will need to be updated. If the device does not have a password or pin to lock the device please set a security code on the device prior to performing these steps.  
  1. Access https://www.digicert.com/CACerts/DigiCertGlobalRootG2.crt on the device.
  2. Click "Download" when prompted to download a file.
  3. When prompted to name the certificate, keep the default values and select "OK."

The trusted certificate should now be installed. To confirm, go to Settings > Security > Trusted Credentials (User tab).  

If the error "Certificate could not be installed because it cannot be read" is received, follow the steps below:
  1. Go to Settings > Security > Install from Storage
  2. Locate certificate file
  3. Click Install