The "" entity type does not exist error while saving node

I decided to try to recreate the node. I was assuming there would be no problem with creating a brand new Basic Page. I copied over some content which includes Full HTML text blocks. I got the page ready, then I went to the other node and deleted it (it still exists in a test environment). Then I hit save on the NEW node/page and got the same error.

I used the same URL alias, which I'm now suspicious of, because that's the only thing that seems to make this node unique. I decided to allow the node to save it using a default URL. It did allow me to save this way (but it deleted all my work).

It appears there is something corrupt about the specific URL alias. I may try deleting it from URL aliases and starting all over.

I looked in URL aliases and there was no longer an alias for the problem node. I went back into the node and changed it to the old URL path. It saved correctly.

I'd like to know why the URL alias could cause such site crashing error while trying to save. I'm willing to move on without a true resolution. If anyone could offer a possible explanation what may have happened, I'd really appreciate this.