Can not upload photos into gallery

Aloha, I created a Gallery for the products on the site I’m managing. This morning I noticed that one of my products had a bad link so after searching I realised that the problem was in the gallery. I deleted the offending product and went to the gallery to rebuild it. When I tried to upload a photo I got a green square with the name of the photo but there was no thumbnail image. In addition the Gallery plugin did not create a block with the products information. So I updated to the latest version of Gallery 4.2.3 and that did not fix the problem. Am I doing something wrong?

Kirk