Error message when trying to upload photos to a gallery saying Itemid cannot be found.

Site URL: https://www.giaconterrazzo.nz

I am going crazy trying to load my new sample photos to my gallery.

I upload the photo okay. Then I go  and edit the content, add name, and tags. When I go to save it it wont. It says  see below???

Taking me hours for a job that should have been finished by now. I tried deleting the image and loading another but that comes up with error 500.

Cant find any info on this anywhere.  Please help.

Adrienne