Unable to download error

I installed Digital Editions (ADE) about a week ago, to be able to download eBooks loaned by our local library,

This worked ok for the first time last week. However this evening I downloaded teo more eBook ".acsm" files, but clicking on either of them causes the error-

Unable to download

Error getting License. License Server Communication Problem:

E_ADEPT_NO_TOKEN

Any idea what could be causing this? My network connection is slow, but it is up and working.