Hey guys,
updated Sponge and Forge to 1515 and the server won’t start anymore. 
There are no other mods on the server.
I’m using: sponge-1.8-1515-2.1DEV-652
[21:35:40] [main/INFO] [Sponge]: /********************************************************************************************************/
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* Oh dear. Something went wrong and the server had to shut down! */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /*------------------------------------------------------------------------------------------------------*/
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* A critical error was encountered while blending Sponge with Forge! */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* Possible causes are: */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* * An incompatible Forge "core mod" is present. Try removing other mods to */
[21:35:40] [main/INFO] [Sponge]: /* see if the problem goes away. */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* * You are using the wrong version of Minecraft Forge. You must use the */
[21:35:40] [main/INFO] [Sponge]: /* correct version of Forge when running Sponge, this version is for */
[21:35:40] [main/INFO] [Sponge]: /* 11.14.3.1515 (you are running 11.14.3.1515) */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* * An error exists in Sponge itself. Ensure you are running the latest version */
[21:35:40] [main/INFO] [Sponge]: /* of Sponge. */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* * Gremlins are invading your computer. Did you feed a Mogwai after midnight? */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /*------------------------------------------------------------------------------------------------------*/
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* Technical details: */
[21:35:40] [main/INFO] [Sponge]: /* */
[21:35:40] [main/INFO] [Sponge]: /* Failed on class : net.minecraft.server.dedicated.DedicatedServer */
[21:35:40] [main/INFO] [Sponge]: /* During phase : DEFAULT */
[21:35:40] [main/INFO] [Sponge]: /* Mixin : server.MixinDedicatedServer */
[21:35:40] [main/INFO] [Sponge]: /* Config : mixins.common.core.json */
[21:35:40] [main/INFO] [Sponge]: /* Error Type : org.spongepowered.asm.mixin.transformer.InvalidMixinException */
[21:35:41] [main/INFO] [Sponge]: /* Caused by : Unknown */
[21:35:41] [main/INFO] [Sponge]: /* Message : Shadow method func_71211_k was not located in the target class */
[21:35:41] [main/INFO] [Sponge]: /* */
[21:35:41] [main/INFO] [Sponge]: /********************************************************************************************************/
-KAISER