Problem when naming conventions in ruby are overriden

Naming conventions for models in ruby on rails are overridden.Entity
User and Responder have many to many association between them.It is
expressed with has many through.

Following are the model files:

user.rb:
has_many :Usertoresponder
has_many :responder, :through => :Usertoresponder

responder.rb:
has_many :Usertoresponder
has_many :user, :through => :Usertoresponder , :dependent => :destroy

usertoresponder.rb:
class Usertoresponder < ActiveRecord::Base
  self.table_name = 'User_To_Responder'
  belongs_to :user
  belongs_to :responder
end

But when saving or getting responder through user there is a problem
occurring it says -
user.responder is not defined.

And the above problem is not occurring when its done using test case
but its occurring if its done through http request.

You're not overriding naming conventions - you're getting cases and
syntax wrong...

Corrected off the top of my head:

user.rb:
has_many :usertoresponder
has_many :responder, :through => :usertoresponder

responder.rb:
has_many :usertoresponder
has_many :user, :through => :usertoresponder , :dependent => :destroy

usertoresponder.rb:
class Usertoresponder < ActiveRecord::Base
self.table_name = 'User_To_Responder'
belongs_to :user
belongs_to :responder
end

BTW What reason is there for not calling the class "UserToResponder"?

Yes class name can be UserToResponder , there is no reason to keep the class name usertoresponder.
Where are the syntax errors?
Same thing is working with test case