Do you have these context settings in your sub.mysite.com/ context:
site_start - Set this to the ID of your "Dev Home" resource.
base_url - Set this to "/" (no quotes) since we’re making the root of the URL our base.
http_host - Set this to "dev.modxcms.com" (or your subdomain name)
site_url - Set this to "
http://dev.modxcms.com/" (or your subdomain url). Don’t forget the trailing slash. Remember this setting is (scheme+http_host+base_url).
please note for my install of 2.0.2, changes to already set context settings will not save. but deleting a setting then adding it back in with the change works