There is a Webform issue which might be similar to this question here. Though that issue is after "upgrading", one could argue that after "upgrade" or after "install" of the module, the result is in both cases that you are using the newest version of the module, right?
So therefore, here are a few things in that issue that might help to get you going:
- Clear the cache and try again.
- if you did something like an update of that module (I think not, but you never know), then run update.php and try again.
- Try to disable and then enable the module, and try again.
Curious to hear if any of this helps ...