Well, I don't really know why that would be happening. But if it was me, I'd first check the accuracy of your original quote. "assets//XML\GameInfo/CIV4PlayerOptionInfos.xml" sounds bogus to me, because of the mixture of double slash, single slash, and backslash. It's a mess. Secondly, I'll check to see if that file exists, and open the file to see if it looks corrupt.
I'd that you make sure you have the latest version of the game — the latest patch from the official civ4 website. If that .xml file is missing or corrupt (and you have the latest patch) then you can get someone to upload their version of the file. It's a pretty ordinary file, so anyone's should do. If that path name with all the weird slash combinations is actually accurate, I'd be interested to know why that was happening. Clearly the only happens sometimes... so it's a bit strange. It could be a Mac specific problem. I know Macs typically use forward slash for path names and Windows use backslash (but often it doesn't actually make any difference). So you could try searching for information about the problem on google or on mac website about games or something.
That's all I can think of at the moment. The patch is the first thing to check.