I did reply this morning (my time), but my reply ain't here. Dunno what happened to it...
Thanks for the help and suggestions. I had another crack at it and solved my issue.
I'm not sure as to the root cause, though.
- I had set ebook-viewer.exe as my default external viewer for several formats
- I uninstalled 0.7.42 and then installed 07.47, rather than updating
- I ran into the problem of not being able to select ebook-viewer as external default anymore
- I tried several methods to rectify this, including uninstalling and reinstalling, as mentioned
- I uninstalled Calibre and rebooted
- I deleted all Calibre folders from Program Files and User Profile
- I ran a registry cleaner (Wise Registry Cleaner)
- Amongst the entries listed as "safe to remove" were several referring to "ebook-viewer.exe"
- I removed these and rebooted, then installed Calibre once more
- Success! I could set "ebook-viewer.exe" as the default external viewer again
Not being a PC professional or MSVP, I can only hazard a guess.
- It appears that setting "ebook-viewer.exe" as the default viewer creates a "sticky" reference in the registry.
- Prior to deleting the "safe to remove" registry entries listed in the registry cleaner, I went and checked books that were in the formats I had set "ebook-viewer.exe" as default viewer for.
- Though "ebook-viewer.exe" had been uninstalled and I had rebooted, the icons hadn't reverted to default - they were still showing the icon from when "ebook-viewer.exe" was installed.