The problem is caused because:
1. The dates the students are eligible for the selected scheme are different from the ones chosen in Curriculum Assignment
2. The students status is not set to accepted.
This can be resolved by clicking on the Relax button on the top right hand corner of the screen.
This will allow the assignment of students to bands regardless of what dates they are supposed to be eligible. However, it may be necessary to address the cause of the ineligibility.