Is this your netbook? Acer Aspire One.
If so it seems you have 2 card readers one standard sd and the second one is SDHC compliant. Here read this snipet from the devices review:
Whichever you choose, you’ll get an 8.9-inch 1024 x 600 LED-backlit display, integrated microphone, stereo speakers and webcam, WiFi b/g and
<b> a memory card slot (capable of reading MMC, SD, MS, xD and other formats). Interestingly, Acer also include a second SDHC slot, intended for more permanent storage </b>
expansion; the multi-format reader is there for quick transfer of files, or viewing photos from your digital camera, while the SD slot means you can add a chunk of extra capacity. This is most useful in the SSD-based Aspire One, obviously.
Try it out in both slots and see if you can get it to work. I assume you are trying to add a chunk of storage to your machine. The SDHC slot is meant more for permanent storage and the sd for cheaper swappable storage.
Let me know how it works out!