Random Number Between Two Numbers VBA

I have build a system that needs a lot of random numbers generated to work.

I have used what I thought would work to generate me these numbers like this example:

VB:
Lastrow = ThisWorkbook.Sheets("RPlay").Range("A" & Rows.Count).End(xlUp).Row
RPlayerNum = Int((Lastrow - 2 + 1) * Rnd + 2)

This would generate a random number into RPlayerNum variable, based on the list in sheet RPlay, missing off row 1 as the header.

However we have noticed a massive flaw in this code.... It works as long as the excel file is open, each time run it gives a different random number. However if you close the excel file and open it, then run it, it ALWAYS gives the same number first run, every time.