A customer cannot change password of the existing user in their account in PBA Control Panel due to the following error message:
Parallels Operations Automation error #error_code #1006, extype_id #41, module_id #AccountManagement, Member not found, username 'user name'
The same error message appears if Provider tries to change password of the problem user in PBA Provider Control Panel.
User mentioned in the error message exists in PBA only, it is absent in POA. PBA is trying to change user password in POA as well, this attempt apparently fails.
Most likely the problem is caused by lack of the 'Additional Staff Members' resource in customer's subscription(s) in POA at the moment when customer was creating new staff member (user) in PBA. In such situation new user will be created in PBA (PBA does not limit number of users in customer accounts) and will not be created in POA due to lack of the required resource (the 'Additional Staff Members' resource limits number of staff members a customer may create in their account in POA).
Refer to the article How to force PBA to re-add a staff member to POA to resolve the problem.