What about the error do you not understand? It says that the "Index exceeds the number of array elements" meaning that indx is greater than the length of ehat array which is 237. That is unless you overwrote the built-in functions rand() and round() with your own functions or variables. Take the semicolon off and see what it is:
indx = round(1+(t-q+1)*UB)
whos indx
whos ehat
estar = ehat(indx);
