Lasso Tool says " Could not fill because there are not enough source pixels on the selected layer."

Hello,

I am new here. I am trying to edit a photo in photoshop by taking small objects out of the image using the Lasso Tool. However, when I go to Edit then to Fill and I have clicked ok it comes up with the following message: 

"Could not fill because there are not enough source pixels on the selected layer."

If anyone is able to help me that would be great! 

Thank you in advance!