I have just encountered a similar problem on my Mac. I bought an ebook which came with ADE. I was able to read it, no problem. Then I upgraded the Mac (after backing up everything) from OSX 10.5.8 to OSX 10.6.8; and now ADE cannot see the ebook, though it is where it should be! Evidently the link has been broken by the upgrade, but how can I repair it?
This is my first venture into the world of ebooks - and I am not impressed!
If it says missing, then ADE can't find the file. You should bring up the info dialog (select it and press ctrl+i) to see where it thinks the file is, and try to look for it there on the old computer.
I'd better explain that with me there's no 'old computer', it's the same one with an upgraded OS. Also, I knew exactly where the file was, though ADE didn't! I had a look round various possible sources of advice on the web; some suggested that I rerun the .acsm file used to install the ebook, but it was not in the ADE directory. I did come across a new version of ADE itself (2.0) so I installed that; and while it was downloading I noticed that the .acsm file I needed was still in the 'downloads' folder. So when ADE was installed, I reran the .acsm file, and a second copy of the ebook appeared in ADE and I could read it! I deleted the 'missing' ebook and all was well.
For future reference, the 'ascm file you saw is not the ebook. It's merely
a pointer to where the ebook is or was stored. DE uses that information to
go and get it. Most of the time, when you're doing a direct transfer, the
'ascm' file will disappear after the ebook has been retrieved by DE