Have you authorised your copy of Digital Editions (ADE) with an AdobeID?
If not, do so in Library dropdown at 'Authorize Computer'
Have you authorised your Kobo Touch from ADE with that ID?
If not, plug in the Kobo and in ADE Library dropdown choose 'Authorize Device'
If either of these fails, there may be some 'residual' authorization information.
To remove old authorization from ADE, ctrl-shift-D (cmd-shift-D on Mac). Restart ADE, and Authorize Computer with you AdobeID.
To remove old authorization from device, plug into ADE and choose ctrl-shift-E (cmd-shift-E on Mac). Restart ADE and Authorize Device.
Please try the below steps and check if that helps: