Urgent: storedProcedure question

I'm currently trying to use a storedProcedure (or rather a function) to 
insert a new row into a database. I got two parameters for my call, one 
being the name of the object to insert and the other one being the 
content (large text to be stored in a blob).

I added a stored procedure to my model and it looks something like this

{
    arguments = (
        {
            allowsNull = Y;
            columnName = i_content;
            externalType = BLOB;
            name = content;
            parameterDirection = 1;
            valueClassName = NSData;
        },
        {
            allowsNull = N;
            columnName = i_name;
            externalType = VARCHAR2;
            name = name;
            parameterDirection = 1;
            width = 255;
            valueClassName = NSString;
            valueType = S;
        },
        {
            allowsNull = Y;
            columnName = 000;
            externalType = NUMBER;
            name = returnValue;
            parameterDirection = 2;
            precision = 10;
            valueClassName = NSNumber;
            valueType = l;
        }
    );
    externalName = WER$FU_CREATEENTRY;
    name = wer$fu_createEntry;
}


So now when I call the procedure the I get a ClassCastException an I 
don't seem to be able to figure out why. Can anyone help me out here?

Regards
Oliver