Hi there,
You need to make sure that the helpers are in this format
domain_name\user_name
domain_name\group_name
Check if the terminal services are allowed through group policy as well as remote assistance runs through TS.
Here's a link to the step by step guide for remote assistance
Step-by-Step Guide to Remote Assistance
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-xp/bb457004(v=technet.10)?redirectedfrom=MSDN
Here is a thread as well that discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
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