.htaccess file is fully writable but unable to save permalinks? Why?

I have a number of WordPress installs running on my local laptop where I develop and test sites before uploading them to a live Internet server.

With all these sites I have no problem saving Permalink changes. But with one I can’t for the life of me get it to save these changes.

All and I mean ALL .htaccess files in ALL WordPress install directories have the exact same permissions (666 I have also tried 777 to no avail on the one problem WordPress install).

All next level up directories are likewise the same in permissions. I even checked the Apache2 named virtual domain files to make sure they too were identical except for the different directories pointed to of course.

Nothing I know explains why the one .htaccess file in the one WordPress install cannot be written to by WordPress! I can even open up the .htaccess file in a text editor and make changes to it just fine.

I am running under Ubuntu Linux.

Anybody got any ideas?

I even installed vs 3.0.1 fresh and it didn’t do any good.

Carlos