How can I use starting and ending index to select from a VARIABLE size vector, in simulink?

For a fixed size vector one can select a part of the vector by start and ending index. But for a variable size vector this does not work. I can only select the 1st element (by applying as index vector [1,1]). If I apply index vector [1,2], the following error pops up:

The second element, 2, at input port Idx1 in 'untitled4/Selector' is not within the range of permissible values (1 through 1) that allows selection of a valid input data element