1. To unlock your mobile memory card, you need a file explorer. You may use FExplorer. To download FExplorer, this is the link http://fexplorer.en.softonic.com/symbian/download
2. After finished downloading, install it to your mobile phone.
3. Insert the mobile memory card into your mobile phone. Remember, don't access the memory card through phone at this moment.
4. Run FExplorer and open the following location C:\system.
5. From the location C:\System, you will see a file named as mmcstore. Rename this file as mmcstore.txt.
6. Copy the file mmcstore.txt. and paste it to your computer. Now, open that file in notepad.
7. When you finished the above steps, you will find the password of that file.
Hope it helped you.