MyProject] /MyProjectName/gen already exists but is not a source folder. Convert to a source folder or rename it
This problem happens when eclipse does not able to find each linked contents in a project.
For example:
When we import a project to eclipse from a specific folder(suppose D://NewFolder), eclipse memorized and link each content with its appropriate path (which is D://NewFolder/project_library/src in our example).
But if we replaced(Here D://NewFolder To E://Another_Folder) or delete the library from its specific folder(Here D://NewFolder), eclipse unable to find its(project_library) original path
and give red error.
So when this problem happens, first we have to make sure that the imported project or library is its original folder and no changes has made to this.
Otherwise again replace the project to its specific folder to which eclipse has linked at the time of import i.e parent folder.