What is this error?

It means that ET tried to reopen etpro-3_1_0.pk3, but failed for some reason. Usually, this means that the pk3 went away (e.g. deleted), but you appear to have a metric assload of pk3s, and deleting some of them (campaign pk3s are the biggest problem) will probably make the problem go away. Since ET appears to hold a file descriptor (handle ) open for every pk3 file, and there’s a finite number of those, having a metric assload doesn’t do you so well.
Is 79 an assload of pk3’s?
And can X-fire be used as a game browser alternative to Gamespy, ASE and Kali?
Or is it’s only like AIM or Messenger for games?