"Autosense failed" - I/O stops on SD card reader

[Bruce Cran]

Hi,

I've been having problems with a card reader (http://www.frontier-electronics.co.za/stor_sdr012.htm) 
and an 8GB SD card 
(http://www.amazon.co.uk/Transcend-SDHC-Class-Flash-Memory/dp/B000P9ZBFA)
I'm trying to use. FreeBSD 9-CURRENT will regularly display the
following error which causes all IO to stop:

(da0:umass-sim0:0:0:0): AutoSense failed
g_vfs_done():da0s1[READ(offset=6782976, length=36864)]error = 5
vnode_pager_getpages: I/O read error
vm_fault: pager read error, pid 2986 (cp)

I tried setting hw.usb.umass.debug=1 but there was no extra debug 
output; setting hw.usb.ehci.debug=1 or hw.usb.debug=1 results in 
lots of output that I'm not sure is useful.
What would I need to do to help debug what's going wrong?

-- 
Bruce Cran