We just met with this problem and wanted to share it with everyone.

When someone wants to move his ruby-project to someone else- he should make sure he did not pass him the folders that begin with "." (dot).
Usually- among all project folders and files, there are two folders that started with the "." character:
.git - the folder that stores the local-repository details (which of course did not need to the other programmer).
.idea - the folder that stores the settings of RubyMine in the current project.

Transfer these folders within the project will cause an error running the project.

Please not.