Clearing the 'external media in unknown state' message
I have experienced similar problems with my Wildfire S and the SD micro card after owning it for just 3 weeks, but I have managed to rectify the 'fault'.
I had swapped the original 2GB card for a reputable brand of 16GB and experienced no problems initially. I also bought a USB adaptor for transferring files to my PC, which worked fine as well. However, today when I replaced the card in my phone after using the adaptor, the "external media in unknown state" notification appeared. Despite unmounting & remounting the card several times and trying to reformat it, the message would not clear.
I removed the card, THEN switched off the phone, removed the battery, replaced the card, replaced the battery, and then switched the phone on. Hey presto, the notification message had disappeared. The 16GB card is now reinstalled and working ok.
Of course, this may be just pure luck, but give it a try and it may just work.