I can't save my SM because split timing was used?

So for a couple tries I was making a steps for my SM file.... It said it couldn't save due to split timing...I don't know why but I exited and re-entered the editor and it was still there... So I thought it was a bug.... I then soon closed step mania as I had other things to do... When I came to edit again it was all gone...
I repeated this 3 times over to make sure... It did the same thing over again....
I want to know what is going on and what the split timing is...?
Please help me....