I've recently encountered a problem where the entrances to buildings don't work. One of these include some objects from Battle Arena, the building is fine, but when you go up to enter it stops you, sort of an "invisible wall" way. How do you fix this?

Did this building you are using come with a .msh.option file?

No, It didn't. I checked the odf file as well and everything is in order.

You might need to create a .msh.option file, with -donotmergecollision in it.

http://beta.xfire.com/videos/5d6f41 - Here is a video of the Battle Arena doing this.

I also looked and there is a msh.option file that went with this.
Are there any other codes that could fix this?

The solution is to build proper collision for the object before exporting and not relying on the game to do it for you. Early versions of 3rd party msh exporting tools (prior to ZE Tools) gave folks the impression that they could skip collision creation. I would import this object into XSI and set up proper collision and re-export.

I see, thank you!