The «end» parameter to Function Sequence is array valued, which is not allowed.
The parameters to Sequence must be scalars.
The function Sequence produces a list of numbers. If one of the parameters is array valued, array abstraction would return many lists, all of differing lengths. If that were allowed, you would end up with a non-rectangular array. Because Analytica does not allow arrays to be non-rectangular, a non-scalar parameter results in an error.
For example, the following would produce this error:
Index N := 5..10
Index J := Sequence(1, N)