Comment 7 for bug 768497

Removed the 32GB and mounted a 1GB:

root@pst007x-aspire-2:/home/pst007x# sudo fdisk -l

Disk /dev/sda: 640.1 GB, 640135028736 bytes
255 heads, 63 sectors/track, 77825 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c5268

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 74766 600555520 83 Linux
/dev/sda2 74766 77826 24573953 5 Extended
/dev/sda5 74766 77826 24573952 82 Linux swap / Solaris

Disk /dev/mmcblk0: 998 MB, 998768640 bytes
20 heads, 51 sectors/track, 1912 cylinders
Units = cylinders of 1020 * 512 = 522240 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0009d5e3

        Device Boot Start End Blocks Id System
/dev/mmcblk0p1 1 1913 975295+ 6 FAT16
root@pst007x-aspire-2:/home/pst007x#

So I can mount and un-mount an SD card as long as there is an SD card inserted on boot up.

I do not believe it is related to the BIOS, because I had windows 7 originally on the PC and never had this issue. For some reason Ubuntu will only detect an internal SD card on this Acer Aspire 5943G if an SD card is inserted prior to boot. Ido not have any issues on other Acer Aspire I have.

Thanks