SendtoUnreal wont work with copies of the project auto created by the launcher.

[The-Maize]

Description: When a project has been duplicated, for the purpose of testing and opening the project in a newer version of the engine, setting the path works file in blender, however by default, the engine names the project with an "illegal" character "." the period in the project name. This will cause the push to unreal to fail. renaming the project without the period resolves this though is still an issue for those that are not able to debug (mainly non advanced or technical users).