I had the same problem trying to read a library E-book.
Wierd - but i solved it by switching from my home wireless broadband to my personal hotspot (Iphone)
Immediately worked like a charm and downloads the pdf using the acsm file.
Scenario 1 Above is with my laptop (Lenovo).
Scenario 2: When I transferred the purchase to my ipad, similar issue of "Document is unavailable at this time". Again, I switched to my hotspot and the thing authenticated.
This whole episode is after i tried:
1. restarting the computer,
2. turning off antivirus,
3. changing the clock time to 2 hours behind, and;
4. contacting the Adobe support, who helpfully told me that ADE is free and hence they can only help with installing and logging into ADE (everything else had to be checked with the E-book developer) Mind you, this step 4 is the recommended final step.
Good luck all and hope this helps.
