I've had what I think is the same problem - Photoshop 2018 CC displays the error dialog, just as it finishes loading the canvas of the file I want to open.
Try this:
1. Open Photoshop and don't open a file. Instead, go to Edit> Preferences> General. After that, head over to the performance tab on the lefthand side. If you get a message saying you must specify "a value between 96 and 8," then we've got the same issue! The issue apparently relates to the way Photoshop interprets the memory available.
2. If this is the same issue, follow the advice found in this forum (Re: Photoshop 2018 Memory Issue) regarding adding a registry key to override the physical memory value. By adding this entry to the registry, Photoshop now works.
Hope this helps.