The face isn't backwards, the issue isn't quite that simple. Simply reversing it will make it visible from the other side, but invisible from the original side.
The issue is that Sketchup displays it's polygons as two sided, visible from both the front and back, while most other 3d programs including NoLimits only displays the front. Polygons are invisible from the back due to a common optimization technique called back-face culling which assumes polygons facing away from the camera will be obscured by polygons closer to the camera, so they can be ignored.
Fortunately you can use the 'Export two-sided' option to fix this without much effort. Read more about Sketchups 2 sided faces and some other things you might need to know about Sketchup here:
http://sketchup.google.com/support/bin/ ... wer=114323
This is a particular pain in simpler programs like Anim8tor where in order to make a simple 2 sided plane you have to make a flat square with 2 triangles than duplicate them and flip the duplicates 180 degrees. Because of this the trees in Silver Mountain which look like 2 simple planes are in fact 4 planes, or 8 triangles. Which makes for more complex texture mapping, particularly if you want them to be symmetrical front-to-back.
Edit: And, naturally, you should always show your models adequate love as they grow, otherwise they may become resentful and end up revealing embarrassing facts about you on daytime talk shows.
Be sure you're not looking in a mirror before you start pointing fingers.