Modified Folder

[oldmanmax]

I have just tried to add something to a folder on a drive, it shows a message of "folder cannot be modified"? I did not do anything to that drive or folder, all other 3 drives have no issue like this, it is not my main drive,it is an external. Drive has a lot of space left on it. What might have changed? I can drag and drop from folder, but not to it.
I am using a G5 PPC, Dual 2.0, Leopard 10.5.2.

 

[swiftaw]

How is the external formatted?

If it's NTFS then you can read it but not write to it.

 

[oldmanmax]

it is Mac OS Extended (Journaled), as all the other drives.
Have been using it for over a year, dragging and dropping what ever I needed. This is totally new occurrence.