[R0B_IX]

I actually had the exact same problem and I wish I knew what fixed it, but I'm not sure. I use gentoo and typically make my own ebuild for calibre since the repository is sometimes slow at updating to the latest versions. Well, with version 40 it gave me the same error and I couldn't think of any obvious solutions. By the time 40 appeared in the official tree, however, (ebuild was basically identical to mine, so nothing new there), it compiled just fine. During that time, there were a few python and PyQt updates, so the solution may be to just reinstall the latest versions of those and rebuild.

I'll try to trace back what was installed and if I come up with an exact solution, then I'll let you know.

[Edit] I should point out that this system is an x86 build.