Hey there,
This means that you need to place a dataview in your layout with the entity type that you use in your snippet and then place the snippet within the dataview.
The snippet in itself does not automatically receive an object and therefor is left wondering where its data is.
By placing a dataview around the snippet containing the entity that your snippet needs, it will be able to receive the necesarry information.
If your snippet already contains the dataview, remove it from there