I have this problem on one of my test machines.
The only solution I can give is to download the AROS Boot Floppy and insert it into the driver when asked.
The problem is, IMHO, caused by the Floppy emulation that we use on the Boot CD. NicJA is/was looking into this problem, as it casues problems in Bochs too.
Out of interest is the Chips set an ALi Magic1? I have nothing but problems with that chipset :-(