Hi,
As per this error given above. <Message>The specified user is either disabled or is not a member of any business unit.</Message>
Please check the user details who is trying to qualify the Lead. As per the error details given above, it seems that the user who is trying to qualify the lead is disabled. Other details that needs to be checked are:
1. User must be enabled and belong to some business unit.
2. User must have a security role that gives permissions to qualify (write) to this specific Lead record.
If above message is generated by a custom business logic then please change the User Context that is used to execute the business logic.
Hope this helps.
Ajay Chawla