beaglebone sd card reader problem, dmesg

root@beaglebone:~# df
Filesystem     1K-blocks    Used Available Use% Mounted on
rootfs           1738184 1144112    504108  70% /
/dev/root        1738184 1144112    504108  70% /
devtmpfs          255280       0    255280   0% /dev
tmpfs             255408       4    255404   1% /dev/shm
tmpfs             255408     236    255172   1% /run
tmpfs             255408       0    255408   0% /sys/fs/cgroup
tmpfs             255408       8    255400   1% /tmp
/dev/mmcblk0p1     71133   55238     15895  78% /media/BEAGLEBONE
root@beaglebone:~# dmesg | grep -i sda
[   33.027070] sd 0:0:0:0: [sda] READ CAPACITY failed
[   33.027085] sd 0:0:0:0: [sda]
[   33.027105] sd 0:0:0:0: [sda] Sense not available.
[   33.027174] sd 0:0:0:0: [sda] Write Protect is off
[   33.027189] sd 0:0:0:0: [sda] Mode Sense: 00 01 10 00
[   33.027248] sd 0:0:0:0: [sda] Asking for cache data failed
[   33.033007] sd 0:0:0:0: [sda] Assuming drive cache: write through
[   33.040175] sd 0:0:0:0: [sda] Attached SCSI removable disk
[   89.025221] sd 2:0:0:0: [sda] READ CAPACITY failed
[   89.025242] sd 2:0:0:0: [sda]
[   89.025263] sd 2:0:0:0: [sda] Sense not available.
[   89.025339] sd 2:0:0:0: [sda] Write Protect is on
[   89.025354] sd 2:0:0:0: [sda] Mode Sense: c0 ff a5 c0
[   89.025415] sd 2:0:0:0: [sda] No Caching mode page present
[   89.031233] sd 2:0:0:0: [sda] Assuming drive cache: write through
[   89.045333] sd 2:0:0:0: [sda] Attached SCSI removable disk
[  122.033056] sd 3:0:0:0: [sda] READ CAPACITY failed
[  122.033079] sd 3:0:0:0: [sda]
[  122.033101] sd 3:0:0:0: [sda] Sense not available.
[  122.033185] sd 3:0:0:0: [sda] Write Protect is on
[  122.033200] sd 3:0:0:0: [sda] Mode Sense: 2f 00 96 c0
[  122.033271] sd 3:0:0:0: [sda] Asking for cache data failed
[  122.039062] sd 3:0:0:0: [sda] Assuming drive cache: write through
[  122.046486] sd 3:0:0:0: [sda] Attached SCSI removable disk
[  155.034997] sd 4:0:0:0: [sda] READ CAPACITY failed
[  155.035019] sd 4:0:0:0: [sda]
[  155.035041] sd 4:0:0:0: [sda] Sense not available.
[  155.035111] sd 4:0:0:0: [sda] Write Protect is off
[  155.035125] sd 4:0:0:0: [sda] Mode Sense: 00 00 00 00
[  155.035185] sd 4:0:0:0: [sda] Asking for cache data failed
[  155.040949] sd 4:0:0:0: [sda] Assuming drive cache: write through
[  155.053165] sd 4:0:0:0: [sda] Attached SCSI removable disk
root@beaglebone:~# mount /dev/sda/ /sdcard
mount: special device /dev/sda/ does not exist
root@beaglebone:~#