How did you ride them before?

In this area nothing has changed in a very long time. If you select "Sit" from the Object Manager then everything should work fine!

If you can't sit on anything then there is an issue. But if you can sit on all other things but just not the horses, then given the fact that you could ride them before then the logical explanation is that something has changed in the horses. It could be that the sit prim is no longer the parent prim or if it's using a script the script is doing something text clients don't like.

I understand what you are saying very well. Let me put this another way:

It works in a viewer because you can see the prim you need to sit on, so you are visually able to select and sit on it. In a text client since you can't see the prim you have to find it if it's not the root prim. Since you can't sit on the horse anymore that means the root prim listed in the top list is no longer the sit prim. You need to ask the creator of the horse why that's the case. To find the sit prim you need to select the root prim for the horse in the top list and the child prims will be listed in "Child Objects" list below it. From there you need to select and try to sit on each child object to find the right one.

There isn't an issue in the sit function so I can't see what else the problem could be related to. It has to be what I've explained above.

See the help page (section 6) below for details:

http://www.metabolt.net/...wiki/ObjectManager.ashx