There are two separate issues with eBooks
- Is the file format .pdf or .epub. (or something else probably not so releavant to ADE or Icarus)
- Is the file DRM protected.
Usually, if a book is available in both .pdf and .epub format, it will be DRM managed or not the same for both formats.
.pdf files are a pain for almost everything except their original pupose of reliable page printing.
Sometimes quite handy for reading cartoon books or children's books which are really layout heavy.
They tend to be particularly troublesome on eReaders (as you have already commented),
which only gets more irritating as time goes on.
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If you can't install both versions at the same time, try just 1.7.2 by itself.
If it recognises the Icarus you will at least by able to register your AdobeID on the Icarus.
Then revert to ADE2.0 and sidecopying if there are extra features of ADE2.0 (such as mutiple vendors) that you really need.