Invalid Array

As Martin already noticed is the reason for this error that the largest value in vector K7 is the last value. Your program then tries to access the values after that element but because its the last value, the values you try to access do not exist - hence the error.

Simple solution is to use an if-statement to deal with that single situation. The loop is only entered when the maximum value is not the last in the vector. Otherwise the vector is returned unchanged.

But its quite inefficient to write a separate program for each of the six variables K2 to K7.

I would strongly suggest to write ONE function (which you could place anywhere above, maybe in a collapsed region) and use this function to calculate the six vectors:

You sure will want to name the function differently 😉

What was your intention with the next calculation?

I guess you wanted to sum up all the values in vector K2, right.?

So you made two errors:
1) you add "j" to the variable "sum", but you do not re-assign the result to the variable "sum". So "sum" remains zero

2) You do not provide a return value, so the program returns the last value it deals with and thats in your case just  the last value in vector K2

Here is a corrected version

But it would be much easier to use the sum operator which Prime offers out of the box (simply don't fill the placeholders at the bottom and the top of the Sigma symbol):