I got the same problem when I used a standard 6 conductor telephone cord. Once I discovered it wasn't wired the same on both ends (2 wires were crossed), I cut off and rewired one end so that it was just like the other end. It worked fine then. You should join the yahoo group for your radio. The address is
http://groups.yahoo.com/group/FT-8800R (616 members)
and
http://groups.yahoo.com/group/Yaesu_FT-8800R (51 members)
If you search the messages on the FT-8800R group, you will find allot of info about the seperation cable. I didn't buy the kit, but I made mine myself for less than $20. It took about 1 1/2 hrs. to do!
See it here:
http://www.radioreference.com/forums/showthread.php?t=20217JRed
KE5FUL