Simulink has no reason to expect that each find() will return exactly one index: as far as it knows, the search could return 0, 1, or several values. That is not acceptable for MATLAB Function Blocks if any acceleration is turned on at all.
When I look at your code, and read your description, I see no reason why
Vscan_start_round(j,1) = V1(d);
should work. You constructed d as min() of an array expression, so d will be a vector, each entry of which is a row index (not array index). You then use those row indices as linear indices into the array, which is bad logic, but in any case will return a vector of values. You then try to store that vector of values into a single location.
If your description was wrong and V1 is a vector then the code would make more sense -- but there would be no point to the code if you can guarantee that exactly one result will be found: since the value to be matched against has been extracted from the vector being searched, if you could guarantee that exactly one value would be found then it would have to be at the location that the data was extracted from, in which case you might as well just use that location directly instead of doing a find()
