I have the latest versions of LR classic and PS CC - 7.1 and 19.1.0. For not apparent reason this morning I get this message whenever i press ommand-e in LR Classic to edit in PS CC. I never had this before nor did I make any changes - still the same camera - Nikon D850 - still using the same Mac and same OS 10.13.3
I "solved" the problem by removing older versions of camera raw on my hard drive - 4.6, 5.x, and 6.7.
The only question I have now is why the message suddenly started popping up.
The message tells you that you are trying to edit in PS3, not PS CC. Do you still have PS3 installed on you computer?
In the Lightroom menu, select Photo>Edit In> Does the Keyboard short cut (Cmd E) indicate Photoshop CC 2018? If it does, try editing through this menu. The next option in the "Edit In" list is Other Application, Keyboard Option:Cmd E. Have you inadvertantly pressed that shortcut?
I still have PS 3 on my computer - just in case. But as I said removing the camera raw that goes with CS3 solved the problem.