Hi guys!!
I had a similar problem with Netbeans 6.5 and finally came up with the solution.
The problem started when I(we) deleted the project from Netbeans, rather closing the project(though the project still exists on the hard drive)
So, this had deleted three folders called "build","dist" and "nbproject" and an XML file called "build".
Solution: Now in order for Netbeans to recogonize ur project as a "project folder" rather than as an ordinary folder, you have to follow the following steps,
Method 1:
Step 1: Create a New project of the same kind(as ur old project, I mean if its Java project create the same).
Step 2: Go to ur newly created project folder on ur hard drive and copy the folders and XML file which were missing, ie.. "build", "dist","nbproject" and an XML file called "build".
Step 3: Paste these in ur old project(which had the problem).
Step 4:Open ur old project as usual in Netbeans.
Method 2
If you have a backup of the project which was once workin fine, then copy those file and folder which were missing and paste them in the present(ur not workin project) and open it as usual from Netbeans.
This worked jus fine for me people and im sure it'll work for u guys too..
I enjoyed the problem
C ya
Subhash Chandra.N.V