I received an "Invalid Tracker ID" error message on the phone.
Check the "Setup..." screen under the AccuTracking menu on the phone:
Make sure you input the tracker ID (a 10 digit number) exactly as it shows up under your "Manage Units" webpage. No space or non-digital characters are allowed in the ID (see here for how to enter numbers on the phone).
The Tracker ID field should take EXACT 10 digits. If the phone wouldn't take the whole 10 digits (i.e. only takes 8 or 9 digits) or would take more than 10 digits, try to exit and restart AccuTracking. If the problem is still there, it might be because the installation is corrupt and you just need to uninstall and reinstall the phone software.