Billchase, don't mount them as harddrives in WinUAE's harddrives tab.
You need to do it like on a real amiga, with C:Mount (or double clicking on the DOSDriver).
If you've already done that, then the problem is MaxTransfer. Edit the CD0 file and change MaxTransfer to 0x1000000
If MaxTransfer isn't in the file, then add it! Then reboot.
If you still have problems, change it to a smaller number.
[Edit] Number is in hex, not dec. Use a decimal to hex converter. 0x1000000 is 16777216 bytes
[Edit2] If 0x1000000 doesn't work, just remove a 0
[Edit3] Yes, remove a 0, 0x100000 is the number to use. Five zeros
Have fun!