FloatProperty Critical Error and other things

[cloudairport]

I was downloading new maps and inserting them into my Infiltration folder tonight, which worked fine the last several times I did so (at least for downloading map packs), but has now caused some sort of Critical Error whenever I try to play Infiltration.

I can get the startup menu to load, but after I click "Play Infiltration" and see the little picture, a tab comes up saying

"Critical Error
Can't find FloatProperty in file
'FloatProperty InfAdds.INFUT_ADD_Turret.FireDistFar'

History: UObject::SafeLoadError <- UGameEngine::Init <- InitEngine"

As far as I know, I didn't do anything unusual when moving the various files into their various folders. So...what did I do wrong and what should I do to fix it? Please, I'm not that tech-savvy, so layman's terms would be appreciated.

I'm running Infiltration 2.9, by the way.

And another thing that I doubt any of you can answer without more information is: Why is it that some of the maps I've downloaded work fine but others don't, saying something along the lines of "Cannot find file package 'x'" whenever I try to launch it?

Thanks for the help.