letting go of a twed disk

-current i386 as of feb 6

while replacing things on a raid array, a new twed unit has
appeared and become un-removable

    # of units: 4
	    Unit 0: RAID 5 931.31 GB ( 1953116672 blocks): OK
	    Unit 1: JBOD 232.83 GB ( 488281250 blocks): OK
	    Unit 5: JBOD 34.47 GB ( 72303840 blocks): OK
	    Unit 6: JBOD 232.88 GB ( 488397168 blocks): OK

    3ware CLI> maint deleteunit c0 u1
    Deleting unit /c0/u1 ...Failed.
    (0x0B:0x0015): Failed to notify os of unit change

looks like the opsys has latched on to it

    # fdisk twed2
    ******* Working on device /dev/twed2 *******
    parameters extracted from in-core disklabel are:
    cylinders=30401 heads=255 sectors/track=63 (16065 blks/cyl)

    Figures below won't work with BIOS for partitions not in cyl 1
    parameters to be used for BIOS calculations are:
    cylinders=30401 heads=255 sectors/track=63 (16065 blks/cyl)

    fdisk: invalid fdisk partition table found
    Media sector size is 512
    Warning: BIOS sector numbering starts with sector 1
    Information from DOS bootblock is:
    The data for partition 1 is:
    sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
	start 63, size 488392002 (238472 Meg), flag 80 (active)
	    beg: cyl 0/ head 1/ sector 1;
	    end: cyl 704/ head 254/ sector 63
    The data for partition 2 is:
    <UNUSED>
    The data for partition 3 is:
    <UNUSED>
    The data for partition 4 is:
    <UNUSED>

is there any way to get the opsys to let go of it so i can
deleteunit it and make it a spare?

randy