ok new issue here. I created a new waterway test for my map, I am using Blender 2.71 with the .X export/Import script taken from 2.69.
now on my pretty much flat plates I can walk over without a problem. but in my next build I created walls. basically trying to make like a waterway that one can walk through. I have included a screenshot, it isn't all that great. but I am in the learning process. taking slow steps.

now with the one that has walls, I can not enter the waterway. it won't let me in. now I know there is bounding boxes around models and such. so is this where I am having problems at? or is it the support for interiors in FPSCR that I am having troubles at.
I am thinking I could just build the base as one model and then add the walls in as another model. but would be much better if I could just create it all as one piece.

now I have been told that the X exporter in 2.71 has issues, and it does, that is why I replaced the x export from 2.71 with 2.69. I dunno if that is where the problem is at either, but on the flatter surfaces exported with same scripts, I can walk over the objects. just not through them if there there are walls. I have created two different style waterways, same problem with both. I am including the first walled waterway in my screen shot, just to give you a idea of what I am doing.

Did you change the collision mode in the FPI file? I believe you need to change it to four, but I might be wrong(btw the collision choices are 1,2,3,4 and they all do something different although im not sure what)

In the FPE file , set
collisionmode = 1

yup that worked, I didn't see collisionmode in the file so I just added it, and it works now. Thank You