pip does not exist or could not be executed within virtualenv
Just had the same problem, which led me here. I had just created a new virtual environment and got that error. Like you, I had an ancestor directory with a space in it. After renaming the directory to eliminate the space, everything worked fine. (Someday I'll track down the bug!) Try changing "Google Drive" to "google_drive" or "GoogleDrive", etc.
First, try install a new and clean virtual environment.
If not work, try installing pip, with easy_install pip