noMthodError with Date Fields and formtastic throws haml error

[monsterag]

NoMethodError (undefined method `to_sym' for {"name"=>"dfgdgdfg",
"datum"=>"12.03.1960"}:HashWithIndifferentAccess):
haml (2.2.9) lib/haml/helpers/action_view_mods.rb:13:in `render'
haml (2.2.9) lib/sass/plugin/rails.rb:19:in `process'

/!\ FAILSAFE /!\ Sat Oct 24 09:37:33 +0200 2009
Status: 500 Internal Server Error
undefined method `to_sym' for {"name"=>"dfgdgdfg",
"datum"=>"12.03.1960"}:HashWithIndifferentAccess
D:/rails/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/
action_view/base.rb:282:in `template_format'
D:/rails/ruby/lib/ruby/gems/1.8/gems/actionpack-2.3.4/lib/
action_view/base.rb:259:in `render_without_haml'

Does anyone have an idea? I allready posted this question to
formtastic group without answer.
tia

[Nathan Weizenbaum]

It's hard to tell exactly what's going on here without any more information, but I'm going to guess this isn't a Haml issue. What's the code in question that's raising the error? Does the error not appear in ERB?