generate securerandom in bouncy castle

[mansour polaris]

hi all

Im trying to use bouncy castle FixedSecureRandom to generate AES key. Before that I tried to use SecureRandom and my code was like this:

            SecureRandom sr = new SecureRandom();
            AESkey = new byte [16];
            sr.nextBytes(AESkey);

the system throws noclassdeffounderror. Then I did obfuscation using Netbeans to the highest level but the problem still.
Then I changed my code to this:

           FixedSecureRandom fsr = (FixedSecureRandom)FixedSecureRandom.getInstance("SHA1PRNG");
            AESkey = new byte [16];
            fsr.nextBytes(AESkey);

the same error is was throwen at first line. Note this code should run in mobile side.

Any idea?Any help?