When you do post to the Audacity forums, be sure to include relevant information about what steps you tried and what errors, if any you encountered.
The steps for exporting from Audacity to .wav format are pretty straight-forward:
File > Export
Click OK
Navigate to the desired output folder
Type a file name
Select WAV from the drop down menu,
Click SAVE
About the only places I can see it having a problem would be if you pick a location that it can't write to or give it an invalid file name.
Have you been able to export in WAV format before and if so, what steps might be different this time? Also, are you using the latest 2.0.3 version, or an earlier version?