E_ADEPT_NO_TOKEN and E_ADEPT_NO_FULFILLMENT_RESULT

I have several installation of Digital Editions.

1. At my primary residence. (Personal Desktop Device #1)

2. At a secondary residence due to travel. (Personal Laptop Device #2)

3. My work desktop (Device #3)

4. My work laptop (Device #4)

I have several books which I have downloaded onto the 4 instances of Adobe Digital Edition. They all work on devices 1,2 and 3.

Today I installed ADE on Device 4.

Of the 5 books, only two loaded. The other 3 books failed with E_ADEPT_NO_TOKEN for one books and E_ADEPT_NO_FULFILLMENT_RESULT for two other books.

I tried downloading the books again. Same result.

I mapped a drive to device 3 and tried to load the books from there, as they installed perfectly on device #3. Same result.

Thus the issue is NOT with the actual ebook files. (*.acsm)

I tried the option to de-authorise device #4 and re-authorize it. Still no success.

Device #4 was ADE 4.5.x whilst Device #3 is ADE4.0. I removed 4.5 and installed 4.0. Same issue.

The issue does not appear to be related to the actual *.acsm files as I tested this with previously installed *.acsm files.

It also does not appear to be related to the client software as I tested 4.5 vs. 4.0

Is there a limit on the number of devices where I can install ADE?

Is there possible a registry issue other than the ADEPT key that needs to be removed etc.?