"Sources directory is already netbeans project" error when opening a project from existing sources

I've installed NetBeans 6.9.1 and installed few updates for it.

Then I've created a new project from existing sources. After a few changes I've closed it. And now I am having an error, when trying to open a new project from existing sources (the same files):

Sources directory is already netbeans project (maybe only in memory).

After Googling it, I noticed it happened not only with me. But I didn't find the correct solution. I've tried to restart the IDE, I've tried to restart the PC, I've tried to reinstall NetBeans. Nothing helped.

Thank you!

I was having the same problem:
Sources directory is already NetBeans project (maybe only in memory).

Netbeans creates a folder in your project named "nbproject". Once you delete that, restart the IDE and you're good to go.

When you create a NetBeans project from existing sources, NetBeans uses the same directory to add its own files: a netbeans folder with .proj files.

Solution: delete the netbeans folder and restart the IDE. Opening a new project should now work.