Personaly, i can see 2 problems with that error report.
java.lang.NoClassDefFoundError: It seems Java can't find your WorldGeneration Class.
Minecraft Textures: You need to register Your Textures for your items / blocks.
for the NoClassDefFoundError, try fixing your packages.
Put this in your IDE src Folder:
assests are for your textures / sounds.
assets/<modname>/textures/blocks
assets/<modname>/textures/items
src code.
<domain backwards>.<modname> or me.<name>.<modname>
if your mods Open Source, please link a GitHub or BitBucket.