Ive actually had the same problem, so i removed Divine rpg and tried it again and i received the same error NoclassfoundDefError and i noticed that it was trying to load it on the client side. i removed all my mods and the server started up fine. I tried to put 1 mod in this time it was ZansMinimap and i received the same error once again. Ive been downloading the latest updates for 1.6.4 of both forge and minecraft along with the mods for 1.6.4 and cant seem to figure it out. Ive been going through the forums and some one said to change the input method from client to server side and that you might need a proxy to do that but i cant figure out how to do that, and i have tried. I then went and deleted minecraft completely and did a fresh install and again the same problems arise. I have had a forge server with mods work in the past on 1.6.2 but eventually got the same problem when i was running biomes o plenty but i finally guessed it must be something with how the forge modloader is trying to run the mods. I always download the latest forge update and retry my process but as of yet nothing has worked. i can post my crash reports or anything if i need to, but i dont believe its only Divine RPG that makes this problem come up.
P.S. i have been inputting the scala libraries manually since they sometimes dont download properly, so idk if it has something to do with the scala files either.