Error: Can't Open project -- Quartus II 6.0

I see the same thing - attrib command forces a removal of the attribute in a way that Explorer does not. Even though the cli attrib command vs explorer properties behaves differently, this is really a Quartus bug in that it errantly does some type of read-only check on the folder that the project is being opened from. Maybe they are doing a check incorrectly using the attribute vs ntfs permissions. Either that, or it is trying to do something subtle to the folder that doesn't result in a tangible modification - maybe some type of locking action? Intel should fix the bug and allow folders with the read-only attribute set to hold projects.

PS, Before anyone tries to claim a read-only folder isn't supposed to have updates, it's standard practice in Windows Explorer for folders to have the attribute set...it's file-level read-only attributes that are meaningful in Windows.