Two possibilities, first is that being a hardware thing, as micro SDHC have a little notch you can easily notice which matches another notch in the reader and that basically just enables it in read-only mode. That you can't change, just try to use another reader or you could put a piece of silicon or tape on notch, easiest thing is to use another reader.
Second possibility is that being a file permission issue, in which case you can do the following :
In terminal, use these commands:
gksudo nautilus
This will launch nautilus in root shell and bypass all permissions.
OR:
sudo fdisk -l
This will give you a list of the drives on your system, figure out which drive it is in the list, easiest way is to look for the blocks as this is the space. It will probably be /dev/sdb or /dev/sdc, then
sudo chown -hR <your username> <the SDHC drive, /dev/sdb for example>
this will change ownership of the drive to you. OR:
sudo chmod -R 777 <the SDHC drive, /dev/sdb for example>
Though if you just execute the first command sudo nautilus it will save you all this trouble, but you'll have to do it every time you use the SDHC.
If all of this doesn't work, use this command :
sudo mount --options remount,rw <the SDHC drive, /dev/sdb for example, find it using fdisk -l>
If there's anything you don't understand just comment.
It sounds to me to be a permissions issue. I've come across this myself with my Linux Mint 14 (Cinnamon) install, which I believe is based on Ubuntu 12.10.
First thing to do is to check the permissions on the hardware device mounting your card. You'll need to find the device name. To do this run the following command:
sudo fdisk -l
Your device will probably be something along the lines of /dev/sdb1, in my case the SD Reader was /dev/mmcblk0p1.
Next you need to get the permissions on this device:
sudo ls -l /dev/mmcblk0p1
Replace "/dev/mmcblk0p1" with your device location.
The output will look something like this:
brw-rw---- 1 root disk 179, 1 Feb 3 21:58 /dev/mmcblk0p1
This tells us the device is owned by User 'root' and group 'disk'
You need to be a member of group 'disk' to be able to write to the SD card.
You can check which groups your a member of with
groups username
In my case I was not a member of the 'disk' group, I rectified this with
sudo usermod -G disk --append username
This adds the group 'disk' to your user's groups, which should allow you to now read & write to the SD card
Best Answer
I had this same problem not even 5 minutes ago. I was trying to figure it out on the forums and googled it and all. After about 40 minutes of searching I decided to try and log out and log back in while the micro SD card and adapter were in the slot. Once logged in I tried to move my files in and it just worked. I heard somewhere in my searches that linux will try and protect the device if it's removed improperly to prevent data corruption, and the only way to fix it is to restart or log back in. Hope it works for you too!