There are lots of bugs in ADE2.0. These include not seeing some eReaders.
Try replacing ADE2.0 with the older but more reliable v1.7.2.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Some eReaders (mainly Sony's) need special drivers installed before ADE will see them, even though they appear on My Computer without.
Not sure if that is true for Kobo Vox, check the instrucrtions that came with it.