Problem with AES 256 algorithm / GCM mode.

[MACH Christian]

Hello.
I use OpenSSL for my work and particularly the AES 256 algorithm with the GCM 
mode.
When I test this mode, the ciphered text is correct but the authentication tag 
is not correct.
I think my test vectors are correct (source : NIST and my cipher room).
Could you help me? If yes, how can we proceed?