Limitation on contentDir?

[magister]

I have eight entries in the contentDir field (each of which is a folder on my Synology NAS). I just tried to add another one, but the "+" button to the right of each contentDir listing is grayed out (the "-" one appears to be live). Is there a maximum of eight? Everything appears to be in order on the NAS -- I was able to log in, create the new directory, move files around, etc.

Thanks - David