[Donald]

I had a problem similar to Matt9876 in post #60 in this thread. Thanks to kovidgoyal for pointing out that post and to Matt9876 for making it. I could however, set file associations to ebook-viewer.exe from C:\Program Files\Calibre2 where the 64-bit version of Calibre is located on my Windows 7 computer, apparently because I had never used it that way. I could not associate the main program though as that is the way I had used it with the 32 bit version, before I uninstalled the 32-bit version.

My fix was similar but more automated. I used the registry cleaner function of CCleaner, noticed at least one left over Calibre mention to be cleaned among the items to fix. I clicked fix all issues and immediately after it finished a few seconds later, when I tried it the main Caliber program appeared just fine in possible programs to associate, e.g. with a mobi file.

I also ran CCleaner's clean function immediately prior to that, which I mention for completeness sake, but I don't think that had anything to do with the fix taking.

I have had great luck with CCleaner by the way, but if you try the program, be aware that when uses the program to clean it will delete files so make sure you uncheck any items you do not want cleaned. An example that most will want to keep, but some will want to delete is browsing history, so make sure to uncheck it if you want to keep it.