Solution
Once a sale date or date removed from production has been entered for a sow, the cycle data can no longer be modified.
To check this:
Go to: '1. Enter/Edit, 1.1. Sows, 1.1.1. Intake/Disposal'
Click on 'Disposed animals' (pig icon with a cross).
Click on 'Search' or press 'F3'.
Enter the plastic ear tag number.
Click on 'Edit'.
Check whether a date has been entered in the 'Disposal date' or 'Date removed from production' field.
If you wish to modify the animal's data, remove the entered date and adjust the cycle data.