Hi,

I finally found what is different from the string read from file and the 
string I manually created. The string from file has an added instance 
variable "@ical_params", which seems to be added by the ical library I'm 
using. The following check in SOAP4R (factory.rb) seems to be the problem:

class StringFactory_ < Factory
   ...

   def obj2soap(soap_class, obj, info, map)
     if !@allow_original_mapping and !obj.instance_variables.empty?
       return nil
     end
     ...

Removing this if-statement causes the problem to disappear. Now I just 
have to figure out why this if-statement is there and what it needs to 
do...

Regards,

Peter