I ran some tests with the following systems:
Computer 1
Distro: Arch
Calibre: 0.8.49 from distro package.
Computer 2
Distro: Xubuntu (Ubuntu with xfce4 as default DE)
Calibre: 0.8.49 from binary install
1st test: I log in C1 but chose icewm instead of xfce4 (it's a humble portable so I don't want to install a full DE like GNOME or KDE). Newsfeeds conversion works flawlessly.
2nd test: I log in C2 with its default xfce (4.8, same as C1). To my surprise conversion works flawlessly also (note that .ICEauthority file is present in all tests). I repeat the test several times with different feeds just to be sure. No error at all.
3rd test: I blame my distro packge, so I remove it from C1 and install the binary download. I log in with my default xfce and (surprise again) ebook generation fails with the error stated at the beginning of this thread.
I'm puzzled. The only conclusion I can draw is that something is not working correctly in the Arch package of xfce4, but there's many software involved to be 100% sure.
Anyway, this settles it for me. I'll just move the damn file (because its generated at every login) before running Calibre and live with it
