Not the biggest thing in the world..

When a comment is placed on an image on tribe, that comment is Cc'ed via Private Message to the person who posted the image.

That PM contains a link to the picture which has been commented on.

When you access the picture via the link contained in the message , you cannot comment on the picture you accessed via the link.

In order to comment, you have to access the picture by going to the tribe and then accessing the picture via the tribe's album, rather than directly from the link within the PM.

In the past, you used to be able to comment after using the link within the PM.

(does that make sense ? Hope so...)