activesupport-3.2.11/lib/active_support/core_ext/hash/conversions.rb has a -- DISALLOWED_XML_TYPES = %w(symbol yaml) -- which is used by its def typecast_xml_value to raise the exception.

I don't see these lines of code in activesupport-3.0.3/lib/active_support/core_ext/hash/conversions.rb

In my case I could upgrade to 3.2.11.

In your case, I am guessing you added the lines of code that disable xml and yaml parameter parsing to an initializer (or application.rb). This way, activesupport simply wouldn't try to convert the parameter value in question into a ruby object.