SMD exporting fail

Hi, i have just learned to use blender for 1 week so this might be a stupid problem for you guys. If so, i have to thank you for your patient and apologize for my carelessly user manual reading.
I was using Blender 2.69 to create an item for dota2. I have the source tools installed and i have succesfully upload the item to the workshop already, but i find it didnt show up in the preview, so i tried to connect the item on the bone of the original hero item and then, export a new smd file.
now, here comes the weird part. i did export a smd file, however, it was a complete blank file. More precisely, the initial cube model that shows up every time when you start Blender.
I tried re install the source tools, and i tried reinstall Blender. I tried the newly released version 2.70 also. one of these fix the problem.
How can I again, export the right smd file again?
So… I hope i make myself clear enough. thank you again for your patient and your help.