I was having trouble with a micro-sdhc card a while back and a program called Chkflsh (I guess it stands for Check Flash) saved me a lot of time and hastle. You can read more about it
here (includes a link to the program).
What I did was set the program to the following parameters.
Access type: Logical Drive*
Action Type: Full Erase
Test Length: One Full Pass
*If the drive isn't seen by windows, select "As Physical Device"
Select your flash card/drive, and click the "Start!" button. After a minute or so, it should be fully erased. Now all you should need to do is eject the drive however you normally do, reinstall it, and it should pop up in explorer. Then use either Windows or the Panasonic formatter program to format it.
Or you could try the
HP USB Formatter tool.
I hope that helps you some. Good luck.
Note: If you use ChkFlsh, the zip file comes with a Danger.bat file. Don't run it unless you want every flash device currently connected to your computer erased. Feel free to delete it as it's only a batch file and not really needed by the program.