mm-build fails and i don't know what to do =/

[optikfluffel]

mm-server works well but if i want to build the project i get the
following Error:
_______
/Library/Ruby/Gems/1.8/gems/middleman-1.2.8/bin/../lib/middleman/
server.rb:182:in `new': undefined method `haml' for
Middleman::Server:Class (NoMethodError)
from /Library/Ruby/Gems/1.8/gems/sinatra-1.2.6/lib/sinatra/base.rb:
1200:in `register'
from /Library/Ruby/Gems/1.8/gems/sinatra-1.2.6/lib/sinatra/base.rb:
1198:in `each'
from /Library/Ruby/Gems/1.8/gems/sinatra-1.2.6/lib/sinatra/base.rb:
1198:in `register'
from /Library/Ruby/Gems/1.8/gems/middleman-1.2.8/bin/../lib/middleman/
features.rb:110:in `activate'
from (eval):52:in `new'
from /Library/Ruby/Gems/1.8/gems/sinatra-1.2.6/lib/sinatra/base.rb:
1211:in `configure'
from (eval):34:in `new'
from /Library/Ruby/Gems/1.8/gems/middleman-1.2.8/bin/../lib/middleman/
builder.rb:35:in `initialize'
from /Library/Ruby/Gems/1.8/gems/thor-0.14.6/lib/thor/group.rb:226:in
`new'
from /Library/Ruby/Gems/1.8/gems/thor-0.14.6/lib/thor/group.rb:226:in
`dispatch'
from /Library/Ruby/Gems/1.8/gems/thor-0.14.6/lib/thor/base.rb:389:in
`start'
from /Library/Ruby/Gems/1.8/gems/middleman-1.2.8/bin/mm-build:9
from /usr/bin/mm-build:19:in `load'
from /usr/bin/mm-build:19

[optikfluffel]

i've found the problem :) i used :ugly_haml in my config without
having it installed xD sorry guys..