Decrypting the Encrypted Data taken from wireshark

I'm using Perl Rijndael(Aes) module to decrypt the Data which is taken from Wireshark. The cipher suite used is TLS_DHE_RSA_AES_256_CBC_SHA. I want to do the same as like wireshark is decrypting the packets.I fed Client write key and Client IV which is taken from the wireshark debug logs to the Perl module.First 16 bytes of the data are not decrypted properly Rest of the bytes are decrypted fine.I have taken the Client write key and IV from the wireshark debug logs.But still can't get the perfect output like wireshark.Where am I making mistake?Anything am I missing? Thanks in Advance