>> mc11._x=300; //this works
>> mc1+i._x=10;//this fails because I add to a object
>> This my problem?
Yes, that's the problem. In the above code, second line,
the value of i to an object referenced as mc1 -- and there
may not even be
such an object, so you're adding i to undefined.
You need to address this object's parent, then use the array
operator to concatenate the string. The "this" property may
do it, or
"_parent" ... it depends on what object(s) you're dealing