There is no Official way on unlocking a Memory card passwords as Passwords are there to protect the Data and if they develop a way for users who forgot the password then that method can be used of unauthorized entry as well.
Before you start I recommend that you back up Everything to you computer by using a memory card reader but if even that is not working then I don’t think you have much options.
1. Go to the mobile phone Menu/Gallery and then scroll down to the memory card. Do not open it yet.
2. Instead, go to Options/ Rename mem. card, enter Select.
3. Delete the old name bypressing Clear several times until the entry is clear.
4. Now, type your desired new memory card name and press OK.
You need to download Fexplorer software (Download from Here or Here) for this procedure. After installation, Browse to c:\system folder in your mobile phone. Here you would find a file named as mmcstore. This file is actually used to store memory card passwords in a mobile phone. Rename this file to mmcstore.txt and open with notepad. You should now be able to read the password in this file.
Go to your phones settings >Security >Phone and SIM> and then allow Remote lock. The password of your remote lock will be the password of your memory card. So if you want to change the memory card password, just send an SMS containing your remote lock message.
If none of the above method work post back on the comments below or on our Forum.