Problem during synthesization

So wordBytes, stackA and byteBits are all constants? My guess is some are signals, which Quartus Integrated Synthesis doesn't accept. I think(emphasize think) you could put this into a for-loop, where the integer goes from one of these values up to that plus 8.

Another concern, if I'm reading this correctly, is that mem_read seems to be some giant vector meant to be a RAM. For example, if you wanted a 256x8 RAM, you just made a signal that is 2047 downto 0 and then access it in 8 bit chunks. If that's what your intent is, I would suggest looking in the Quartus II Handbook at HDL coding guidelines for inferring a RAM, which is normally done with an array, so that the width is much more explicit than just inices that are i to i+8. I'm just taking a guess what you're doing, so ignore if that's not relevant.