Here we are. Safe mode. No Firefox. Still takes forever.
And here is the process explorer output.
I did get the library onto another machine and ran it there.
No trouble at all.
So without doubt it is a Windows problem or, we could say I suppose, a possible windows/calibre conflict. There's not just me experiencing this.
Anyway here is the process explorer output for that session in safe mode.
It'll be lovely if it reveals something to someone somewhere, this is a real hassle.
