Hello,
Do we understand correctly that the backup script is executed in a Windows Scheduled Task? Could you, please, specify credentials of what account are specified in the security settings of the task? Is it the credentials of the Adaxes service account (specified during Adaxes installation)?
Also, could you, please, post here or send us (support[at]adaxes.com) the script you are using? Does the script use the credentials of the Adaxes service account?