Regarding the Trim tool
 

Hi, I need to use the trim tool on the surface shown in the image but for some reason it is not working. The curve that's projected onto this surface is selected in the image. When I evoke the trim tool and try to select this surface no trimming takes place that is, it doesn't get converted into a white wire frame as it normally should. This isn't the first time it's happening like this. And I am using Maya 7.
Could any one tell me why it isn't working?
Any suggestion will be appreciated.
T.

Hi, I managed to trim the surface by increasing the tolerance value for the trim tool. Don't see why though. The curve-on-surface goes from one edge to the other. I don't know what tolerance has got to do with it though.