trouble with export of .stl file

Are there some weird limitations on exporting .stl files? I cannot export some .blend files, but simple ones with cubes or icospheres or such things will export. Am I missing something? All I get is “can’t write file” if Blender balks. When I check the console I see no error messages. Using 2.49b on OS X 10.5.7. Downloaded a fresh copy and still same issue. I want this for 3D printing uses, although I can apparently get by with COLLADA export.

I’ve checked for doubled vertices and non manifold instances, but none exist. The model is not that large, under 20000 polygons. All triangles. Thanks for any advice.

I am having a similar issue, only that all of my exports are exported as cubes…
and are the same file size (64 bytes)