Eclipse is looking for eclipse projects, meaning its is searching for eclipse-specific files in the root directory, namely
.classpath. You either gave Eclipse the wrong directory (if you are importing a eclipse project) or you actually want to create a new project from existing source(
create project from existing source).
I think you probably want the second one, because Eclipse projects usually have separate source & build directories. If your sources and .class files are in the same directory, you probably didn’t have a eclipse project.