Hmm....check Run-->Run Configurations and make sure Client is:
net.minecraft.launchwrapper.Launch
...and Server is:
cpw.mods.fml.relauncher.ServerLaunchWrapper
Also, please make sure your Eclipse Workspace is forge/mcp/eclipse and *not* forge/fml/eclipse
(Project-->Properties, then Resource.Location)
Mine is forge\mcp\eclipse\Minecraft