Can’t access the partition that OS is denied

Can someone please help me figure out why when you try to upgrade your win2000 server to 2003 your attempts to access the partition that has the OS is denied unlike before. And also, why is it during the text-mode part of setup there is a probability of getting a stop error message that looks like this; STOP: 0x0000008E(0xC0000006, 0xFC99F5C0).
