Problems connecting a (formerly working) flash device

[Tino Engel]

Dear beasties,

I have a problem with a flash device (1G, FAT).
It did not work on a special usb-hub on my system. Connecting it to 
another hub, I was able to access the device and load data to it.
The only irregularity was that on connecting the device not only 
standard /dev/da0 and /dev/da0s1 were created, but also two "dummy" 
devices/dev/da0s2 and /dev/da1. But that made no problem in mounting 
/dev/da0s1 as usually using mount_msdosfs.

Today I wanted to mount the device again and it fails now on any 
usb-port, always sending the same error message to dmesg.

uhub2: device problem (INVAL), disabling port 5
uhub2: device problem (INVAL), disabling port 7
uhub2: device problem (INVAL), disabling port 6
uhub2: device problem (INVAL), disabling port 5
uhub2: device problem (INVAL), disabling port 1
uhub2: device problem (INVAL), disabling port 1

 (I tried connecting to various ports)


After various reconnects, I was able to get the device mounted again, 
resulting in dmesg as follows:

<snipped all before>
umass0: <SanDisk Sansa e250, class 0/0, rev 2.00/7.20, addr 2> on uhub2
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <SanDisk Sansa e250 \\000\\001> Removable Direct Access SCSI-0 device
da0: 40.000MB/s transfers
da0: 1917MB (3926016 512 byte sectors: 255H 63S/T 244C)
da1 at umass-sim0 bus 0 target 0 lun 1
da1: <SanDisk Sansa e250 \\000\\001> Removable Direct Access SCSI-0 device
da1: 40.000MB/s transfers
da1: Attempt to query device size failed: NOT READY, Medium not present
(da0:umass-sim0:0:0:0): SYNCHRONIZE CACHE. CDB: 35 0 0 0 0 0 0 0 0 0
(da0:umass-sim0:0:0:0): NOT READY asc:3a,0
(da0:umass-sim0:0:0:0): Medium not present
<snip: a couple of times repeating this message>
(da0:umass-sim0:0:0:0): SYNCHRONIZE CACHE. CDB: 35 0 0 0 0 0 0 0 0 0
(da0:umass-sim0:0:0:0): NOT READY asc:3a,0
(da0:umass-sim0:0:0:0): Medium not present
GEOM_LABEL: Label for provider da0s1 is msdosfs/Sansa e250.
(da0:umass-sim0:0:0:0): SYNCHRONIZE CACHE. CDB: 35 0 0 0 0 0 0 0 0 0
(da0:umass-sim0:0:0:0): NOT READY asc:3a,0
(da0:umass-sim0:0:0:0): Medium not present
<snip: a couple of times repeating this message>
(da0:umass-sim0:0:0:0): SYNCHRONIZE CACHE. CDB: 35 0 0 0 0 0 0 0 0 0
(da0:umass-sim0:0:0:0): NOT READY asc:3a,0
(da0:umass-sim0:0:0:0): Medium not present
GEOM_LABEL: Label msdosfs/Sansa e250 removed.

Now I can mount the device using mount_msdosfs /dev/da0s1 /mnt.
freebsdangel# ls /dev/da*
/dev/da0        /dev/da0s1      /dev/da0s2      /dev/da1
freebsdangel#
               
 From my shell:

Anyone has an idea how to debug this error, as soon as it occurs again?
I have googled and searched the archives, but the error message seem to 
be related to various different problems.

Rg, Tino