Click on "upload" near the top of this page, just as if you wanted to post a new scene. You will then be presented with the upload page where you enter information about your scene. At the bottom of that page you will see a box labeled "Group". You click on the arrow next to that box and then you select the group that you want your scene to go into. If you do not click on a group, then your scene will be placed in the "default" group. You have uploaded many scenes over the past few months. Don't you even have a clue what a group is?
Anyhow, I think that you accidentally selected a group which is not allowed, so just go ahead and select the Marble Race group instead. After you enter all the other information about your scene, it should then upload to Algobox.
Oh, you probably use the Algodoo browser for uploading and downloading scenes. I assumed that you use a browser like Internet Explorer or Chrome, etc. That's why you don't see UPLOAD!
Well, in that case I don't know what can cause the wrong group to be selected. I'll ask someone else to see if he knows what can cause that. In the mean time, maybe someone else who knows about the Algodoo browser can help you.
Hazevision550 - I asked for help with this issue in the Algodoo FORUM. So, hopefully within a couple of days someone will see my request for help and they will respond to you.