SimilarityMeasure initialization problem

HI all,

I have a dataset with an id column of type "text" named "att24754".
I have a problem with initialization of Cosine similarity measure. Calling the following code:

clusteredSet=clusteredSetInput.getData(ExampleSet.class);
similarityMeasure= new CosineSimilarity();
similarityMeasure.init(clusteredSet);

Now the problem is come up in calling init "method":

"The example set contains non-numerical attribute att24754 which is not allowed for value based similarities."

and the strange thing is that "att24754" has set to the "id" of my exampleset. So I expect it to not be involved in similarity calculation as an "special attribute". But it will be involved in the similarity computation and so RM generates the error. I know all of the attributes should be numerical except my id. Does anyone know what's going wrong here?

Any idea would be greatly appreciated.

thanks.