Unable to share any folder, "Incorrect function"

When I try to share a folder, I receive this error message:

"An error occurred while trying to share xxx. Incorrect function.
The shared resource was not created at this time."

This happens with every folder I try to share.

In computer management when I try to add a share, I get the same error:
"The folder could not be shared for the following reason:
Incorrect function."

Also, in the Network and Sharing center, when I turn on Public folder
sharing, I get the same "Incorrect function" error.


I've already shared folders some time ago, and they still work. I can remove
a share, but not add new ones, so it must be a setting or something like that
I screwed up...

I did a search on google, but found one forum post about somebody with the
same problem, but no information about how to solve this.
Does somebody know about this problem and how to fix it?