Adding objects to cloth modifier HELP!

Hey,

I am trying to add simulation properties (0 for collsion, 1 for cloth) to objects in a cloth modifier I have on a plane object. I can add the objects to the modifier but when I try to set whether they are a collision object or a cloth object I get the following error when running the script: --Runtime error: Error, object is not part of simulation

Any ideas on how to fix this because I have no clue at this stage!

Thanks