I have bought this one: 8GB ADATA micro SDHC (AUSDH8GCL6) (Class 6)
as I saw is compatible with RB450G http://wiki.mikrotik.com/wiki/Supported_Hardware#Memory_cards
But whe I go to system>stores I se microSD as invalid. Everytime I try to format it, router disconects 
Is there any trick to make it work?
Thanks
None?
Try with latest RouterOS versions. I noticed that something has changed to RouterOS 5.0RCs, since my 433AH now identified and formatted one sandisk card that not worked with some 4.x version when tested long time ago.
But I don’t see much usage for it, because it is quite slow reading and writing cards.
Just mark the card and hit format in winbox
when I do that, router disconnects from PC. I have used 4.17 and 5.0 but microSD is invalid.
Hi All,
I went through the same story a while back,
ROS 4.17 does not want to recognize the SD card,
Upgraded to ROS RC5.06 I think at that time and got it to work,
downgraded back to ROS 4.17 and SD card was still working.
Upgraded to ROS 5.1 and card is missing…
Now I need to get the cad up and running somehow…
The same problem
mikrotik 450G + Transcend 4 GB SDHC (TS4GUSDC6)
hm, strange
аll other devices work with this card
I got the same problem.
I tried 2 microsd card, one is sandisk 1G, the other one is sandisk 4G
The 1G shows invalid, but can be formatted, then works fine.
The 4G card, just like those described in the previous posts, failed…
I end up put the 4G card in a card reader, then format it to ext3 in a linux box.
then it works fine 
Even if the card model is supported, there could be a different revision of the card (another batch) and maybe yours is not supported. So try another type of card, maybe you have an unsupported model after all.