This is the response I received from MS when my one care would not start,
you might give it a try, it worked for me.
From you description, I understand that an error message "One Care backup
encountered a problem and cannot
start. Click get help for assistance." was received when attempting to
perform a backup. If I have misunderstood, please do not hesitate to let me
know.
I understand the inconvenience you have experienced. Please be assured that
I will do my best to help you.
This issue can be caused by the corrupted Windows Live OneCare backup
engine. Let's try the following steps to rebuild OneCare backup engine.
Step 1: Use Windows Installer Cleanup utility
=============
1. Please download and install the Windows Installer Cleanup utility from
this link:
http://download.microsoft.com/download/E/9/D/E9D80355-7AB4-45B8-80E8-983A48D5E1BD/msicuu2.exe
Note: although it is released as a Microsoft Office update, it can be used
to fix Windows Installer.
2. Then, please run it from Start-> All Programs-> Windows Install Clean Up.
3. Please select "PX Engine" and click "Remove".
Step 2: Manually install PX Engine
==============
1. Click Start, click Run, type "%programfiles%" (without quotation marks)
in the open box and then click OK.
2. Open the Microsoft Windows OneCare Live folder.
3. Locate and open the Staging folder.
4. Double click "PxEngine.msi" to reinstall it.
5. After that, it will prompt to restart the computer.
