The subject error is the result of the Expert not having proper permissions on the Novice's computer.
To fix the problem:
1. Start / Run / gpedit.msc / OK.
2. Double-click Offer Remote Assistance at Computer Configuration / Administrative Templates / System / Remote Assistance.
3. Make sure that the policy is Enabled.
4. Press Show.
5. Make sure that the Expert is listed in the Helpers group, and that their ID is not misspelled.
6. See Online Help to view the RSop (Resultant Set of Policies) to determine if a domain push is causing the problem.