Simple block mod can't run on a server

Can you post your crash log?

Which version of MCreator did you use to create this mod?

Are you sure your mod only adds new recipes?

Class of your block uses references to client-only classes in the common or server-side code, resulting in to crash, as the server-side cannot see these classes as they de-facto are not there.
The client-side class is EntityClientPlayerMP. You have to use some common or server-side class instead, depending on your needs. I do not have an access to your code, but I guess that using EntityPlayer should be enough, if it is possible in the method, that the EntityClientPlayerMP is referenced from. Another possible solution could be checking for server-side (using field isRemote (its value is false for a server) in World class) and/or using @SideOnly annotation.

I can not offer any more help as long as you don't provide any of your code, as it is nearly impossible to do anything without it.

Replace 

public void onBlockAdded(World world, int i, int j, int k) {
            EntityPlayer entity = Minecraft.getMinecraft().thePlayer;
            if (entity != null && world != null) {
                int le = MathHelper.floor_double((double) (entity.rotationYaw * 4.0F / 360.0F) + 0.5D) & 3;
                world.setBlockMetadataWithNotify(i, j, k, le, 2);
            }
 
            world.scheduleBlockUpdate(i, j, k, this, this.tickRate(world));
 
        }

by this

public void onBlockPlacedBy(World world, int i, int j, int k, EntityLivingBase entity, ItemStack stack) {
            if (entity != null && world != null) {
                int le = MathHelper.floor_double((double) (entity.rotationYaw * 4.0F / 360.0F) + 0.5D) & 3;
                world.setBlockMetadataWithNotify(i, j, k, le, 2);
            }
 
            world.scheduleBlockUpdate(i, j, k, this, this.tickRate(world));
 
        }

And you should be fine.

You have to import EntityLivingBase class, you can do it manually (import net.minecraft.entity.EntityLivingBase;), or you can use the fix imports button. (Actually that is not its name, but it is close enough. Most likely something like "fix imports & format code".)

I have not modded for 1.7.10 for quite a while, but it seems that MCreator for this version most likely generates this part of the code for every new block. So you have to do this change for every new block, I guess. Alternatively, you could also just remove the part of the code. What the code actually does is that it sets the metadata f the block based on placer facing on its placement, so if you do not want to have the block this functionality, you should be fine without it.