Thresholds are values that limit the amount of changes between imports. If academicSessions has a threshold of 2, then only a maximum of two values are allowed to be added, modified, or removed from academicSessions.CSV.
In order to understand the differences between the two sets of files (the originals and the ones pending import) click on the "Show Actions" button underneath the Error Details report.
This specialized error report can be reached by the following steps:
1) Enter the Import Rosters tab
2) Click on the most recent import which exceeded thresholds
3) Scroll down to the Error Details list and click "Show Actions"