When you need to edit or remove a data entry, there are a few items that might be unavailable to edit ou remove:
That happens usually because that data entry is not the last data entered in that sow or group.
On those cases you can check accessing the sow card or de group card, go to history and check if that data was the last entry there was.
For instance, the sow 99123 you can see a weaning and than a mating.
Therefore to edit the weaning date, you would have to go through the following steps:
1 - Remove the mating
3 - Edit the date of the weaning or any other data you need to adjust
4 - Add back the mating
Than you can check that the sow card is changed: