In the expression X.J, Variable X is not indexed by J. In the expression «expr».J, the result of «expr» is not indexed by J.
An Analytica expression of the form A.I refers to an index named «I» of the array «A». It is often used to refer to local indexes, since in the case of a local index, you cannot simply use the identifier
I where an index is expected because the local index does not exist in the global namespace. A local index can only be accessed by using this syntax starting with an array that has that index. This error occurs when the value in question is not indexed by «I».
This probably exposes an error in your logic.