The drush subtheme wizard cannot find the Omega base theme.

The following shows the subtheme generation process in terminal, and the error at the bottom. Omega 4.x is installed and enabled in the sites/all/themes directory of my local site. The same error occurred when I tried using the default starterkit and keeping the readme files.

KENDALLs-MacBook-Pro:omega-four kendall.totten$ drush omega-wizard
Please enter the name of the new sub-theme [Omega Subtheme]: test
Please enter a machine-readable name for your new theme [test]: test
Please choose a base theme for your new theme
[0] : Cancel
[1] : amazon (Subtheme of Omega)
[2] : extended (Subtheme of Omega)
[3] : Omega
[4] : quad (Subtheme of Omega)

3
Please choose a starterkit for your new theme
[0] : Cancel
[1] : Extended: This is a short description for the Extended starterkit. (Provided by Omega)
[2] : Default: This is a short description for the Default starterkit. (Provided by Omega)

1
Please choose a destination. This is where your sub-theme will be placed
Please choose a destination type.
[0] : Cancel
[1] : Site (e.g. 'all' or 'example.com')
[2] : Installation profile
[3] : Parent theme

1
Please choose a site.
[0] : Cancel
[1] : all
[2] : omega-beta

1
Do you want to keep the starterkit's readme files? (y/n): n
Do you want to enable your new theme? (y/n): y
Do you want to make your new theme the default theme? (y/n): n
Where is the Omega base theme? I has not found it. :(