On a Macintosh computer the folders on the hard drive that are accessed by Design Manager Online are treated as shared network folders since DM must load or save such files over the Internet (a network). Cross/platform shared network folders on a Mac cannot contain spaces in the files names. Rename folders on the Mac that you wish to access with DM Online so that the folder names do not include spaces.

See the following for more information: http://support.apple.com/kb/HT2799?viewlocale=en_US