This is an old thread but I also I had the same error now and the title says it all. Only that in my case I updated something that I’m using and because it was now in a different location as the folder name contains the version, I was pointing to the wrong folder. What helped me was reading the log located: Project Folder\Saved\Logs. There look for the last file that was created (ProjectName.log). And inside it were 2 lines that pointed to the problem:
LogWindows: Failed to load 'ProjectLocation/ProjectName/Binaries/Win64/UnrealEditor-ProjectName.dll' (GetLastError=126)
And the next line after that which for me was a clear indication:
LogWindows: Missing import: DllName.dll
And so in my case I had to change to the new location, and removing Binaries and recreating them wouldn’t have helped.