This error occurs when there are duplicate enrolments in a subject unit. For instance 3 students are enrolled in 2 classes but are only attending one.
This is the message you will receive
To resolve the issue do the following
1. Go to Main Menu select Education then Subject Units
2. Enter the Subject Unit Code in the Search field
3. Select Edit Subject Unit identify the duplicate enrolments in the Enrolment pane
4. Then select the Set Reporting and select No to AVETMISS Reporting