Problem with "Snakebitten" Achievement

Time: I don't remember exactly when it was.
Frequency: always.
World name: Ragnarok.
Character name: Neoeden Nereruo.
NPC name: "Serpent Personnel Officer".
Monster name: no monster for this issue.
Class/Level: I was ACN level 20 and after WHM level 50 (see the steps below).
Party or solo: solo
In-game time: as Earth time, i don't remember it.
Area and coordinates: New Gridania (9,11).
Steps:
1. I've choose the Grand Company "Order of the Twin Adder" when the Main Scenario Quest asked to me. No achievement unlocked at that time. (ACN 20)
2. I've raised my rank in Grand Company till the maximum aviable "Second Serpent Lieutenant".
3. After a few months I've choose to change my Grand Company; before Maelstrom and then Immortal Flames. Both achievement of enlist with Lominsan and Uldhan Grand Company were unlocked (respectively "All Watched Over by a Maelstrom of Loving Grace" and "Light My Fire"). (WHM 50)
4. I've raised my rank in both Grand Company till the maximum aviable, respectively "Second Storm Lieutenat" and "Second Flame Lieutenat".
5. Then dedcided to go back to Gridanian Grand Company and even if I've forced the enlistment, the achievement "Snakebitten" is still locked. (WHM 50)
Now I stay in Gridanian Grand Company.

Connection Specs
- Type of internet connection/provider: ADSL, Telecom Italia S.p.A.
- Modem maker/model number: Aliuce Gate VoIP 2 Plus Wi-Fi

PC Specs
-=-=-=-=- System Information -=-=-=-=-
SYSTEM_OS Windows 7 Professional 32 bit (6.1, build 7601) Service Pack 1 (7601.win7sp1_gdr.130828-1532)
SYSTEM_CPU Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz (2 CPUs), ~2.9GHz
SYSTEM_CORE_NUM SYSTEM_CORE_LOGIC 2 SYSTEM_CORE_PHYSICS 2
SYSTEM_BIOS BIOS Date: 08/05/09 16:33:17 Ver: 08.00.14
SYSTEM_LANGUAGE italiano (Impostazioni internazionali: italiano)
SYSTEM_MEMORY 3327.117MB
SYSTEM_VIRTUAL_MEMORY 2047.875MB
SYSTEM_PAGE_FILE 6652.523MB
SYSTEM_STORAGE C:\ SYSTEM_HARDDISK_DRIVE SYSTEM_TOTALDISC_SPACE 108.803GB SYSTEM_FREEDISC_SPACE 73.350GB
SYSTEM_STORAGE D:\ SYSTEM_HARDDISK_DRIVE SYSTEM_TOTALDISC_SPACE 82.000GB SYSTEM_FREEDISC_SPACE 78.186GB
SYSTEM_STORAGE E:\ SYSTEM_HARDDISK_DRIVE SYSTEM_TOTALDISC_SPACE 41.983GB SYSTEM_FREEDISC_SPACE 41.893GB
SYSTEM_STORAGE H:\ SYSTEM_HARDDISK_DRIVE SYSTEM_TOTALDISC_SPACE 931.503GB SYSTEM_FREEDISC_SPACE 332.214GB
SYSTEM_DIRECTX_VERSION DirectX 11
SYSTEM_GRAPHICS AMD Radeon HD 5700 Series
SYSTEM_GRAPHICS_DEVICE \\.\DISPLAY1
SYSTEM_GRAPHICS_CHIP AMD Radeon Graphics Processor (0x68B8)
SYSTEM_GRAPHICS_MAKER Advanced Micro Devices, Inc.
SYSTEM_GRAPHICS_VRAM 1018.582 MB
SYSTEM_GRAPHICS_SHARED_VRAM 1407.559 MB
SYSTEM_GRAPHICS_DAC Internal DAC(400MHz)
SYSTEM_GRAPHICS_DISPLAY_MODE 1600 x 900 (32 bit) (60Hz)
SYSTEM_GRAPHICS_DRIVER aticfx32.dll,aticfx32.dll,aticfx32.dll,atiumdag.dll,atidxx32.dll,atiumdva.cap
SYSTEM_GRAPHICS_DRIVER_VERSION 8.17.0010.1247
SYSTEM_GRAPHICS_DRIVER_DATE 07/12/2013 00:00:42
SYSTEM_GRAPHICS_DRIVER_LANGUAGE Inglese
3.0
SYSTEM_GRAPHICS_PIXEL_SHADER 3.0
SYSTEM_GRAPHICS_VERTEX_TEXTURE SYSTEM_SUPPORT
SYSTEM_GRAPHICS AMD Radeon HD 5700 Series
SYSTEM_GRAPHICS_DEVICE \\.\DISPLAY2
SYSTEM_GRAPHICS_CHIP AMD Radeon Graphics Processor (0x68B8)
SYSTEM_GRAPHICS_MAKER Advanced Micro Devices, Inc.
SYSTEM_GRAPHICS_VRAM 1018.582 MB
SYSTEM_GRAPHICS_SHARED_VRAM 1407.559 MB
SYSTEM_GRAPHICS_DAC Internal DAC(400MHz)
SYSTEM_GRAPHICS_DISPLAY_MODE 1920 x 1080 (32 bit) (60Hz)
SYSTEM_GRAPHICS_DRIVER aticfx32.dll,aticfx32.dll,aticfx32.dll,atiumdag.dll,atidxx32.dll,atiumdva.cap
SYSTEM_GRAPHICS_DRIVER_VERSION 8.17.0010.1247
SYSTEM_GRAPHICS_DRIVER_DATE 07/12/2013 00:00:42
SYSTEM_GRAPHICS_DRIVER_LANGUAGE Inglese
3.0
SYSTEM_GRAPHICS_PIXEL_SHADER 3.0
SYSTEM_GRAPHICS_VERTEX_TEXTURE SYSTEM_SUPPORT
SYSTEM_SOUND Altoparlanti (Realtek High Definition Audio)
SYSTEM_SOUND_DEVICE_ID {6A25F5ED-A29C-4A7F-ADFF-349A05919903}
SYSTEM_SOUND_DEVICE_NAME RTKVHDA.sys
SYSTEM_SOUND_DRIVER_VERSION 6.00.0001.5859
SYSTEM_SOUND_DRIVER_LANGUAGE Inglese
SYSTEM_SOUND_DRIVER_DATE 22/05/2009 20:03:40
SYSTEM_SOUND Headset (Sound Blaster Tactic(3D) Alpha)
SYSTEM_SOUND_DEVICE_ID {3BFBA620-A083-4041-B24A-F1DAF75B0F84}
SYSTEM_SOUND_DEVICE_NAME USBAUDIO.sys
SYSTEM_SOUND_DRIVER_VERSION 6.01.7601.18208
SYSTEM_SOUND_DRIVER_LANGUAGE Inglese
SYSTEM_SOUND_DRIVER_DATE 12/07/2013 12:07:52
SYSTEM_SOUND Realtek Digital Output (Realtek High Definition Audio)
SYSTEM_SOUND_DEVICE_ID {B3D3933A-7A3D-409E-B55C-D5A620A072F0}
SYSTEM_SOUND_DEVICE_NAME RTKVHDA.sys
SYSTEM_SOUND_DRIVER_VERSION 6.00.0001.5859
SYSTEM_SOUND_DRIVER_LANGUAGE Inglese
SYSTEM_SOUND_DRIVER_DATE 22/05/2009 20:03:40
SYSTEM_SOUND Realtek Digital Output(Optical) (Realtek High Definition Audio)
SYSTEM_SOUND_DEVICE_ID {F5E65296-A06B-4E13-AC72-F2F97921EF56}
SYSTEM_SOUND_DEVICE_NAME RTKVHDA.sys
SYSTEM_SOUND_DRIVER_VERSION 6.00.0001.5859
SYSTEM_SOUND_DRIVER_LANGUAGE Inglese
SYSTEM_SOUND_DRIVER_DATE 22/05/2009 20:03:40
SYSTEM_INPUT {6F1D2B60-D5A0-11CF-BFC7444553540000}
SYSTEM_INPUT_NAME Mouse
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 3 SYSTEM_GAMEPAD_BUTTON 5 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {6F1D2B61-D5A0-11CF-BFC7444553540000}
SYSTEM_INPUT_NAME Tastiera
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 128 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {3852DE40-AD0A-11E3-8001444553540000}
SYSTEM_INPUT_NAME Sound Blaster Tactic(3D) Alpha
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 1 SYSTEM_GAMEPAD_BUTTON 0 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {385C2D10-AD0A-11E3-8002444553540000}
SYSTEM_INPUT_NAME Sound Blaster Tactic(3D) Alpha
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 0 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {385C2D10-AD0A-11E3-8003444553540000}
SYSTEM_INPUT_NAME Mouse USB hardware Microsoft
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 4 SYSTEM_GAMEPAD_BUTTON 1025 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {3862BCC0-AD0A-11E3-8004444553540000}
SYSTEM_INPUT_NAME Gaming Keyboard G110
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 7 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {3864B890-AD0A-11E3-8005444553540000}
SYSTEM_INPUT_NAME Gaming Keyboard G110
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 0 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {3864DFA0-AD0A-11E3-8006444553540000}
SYSTEM_INPUT_NAME G110 G-keys
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 0 SYSTEM_GAMEPAD_FOV 0
SYSTEM_INPUT {38652DC0-AD0A-11E3-8007444553540000}
SYSTEM_INPUT_NAME G110 G-keys
SYSTEM_INPUT_REMARKS SYSTEM_GAMEPAD_AXIS 0 SYSTEM_GAMEPAD_BUTTON 0 SYSTEM_GAMEPAD_FOV 0
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Browser Information
- Name and version of the browser currently in-use: Mozzilla Firefox 28.0
- Internet Explorer Version: 11.0.9600.17105 (update version: 11.0.7 KB2964358)

just like your bug with My Little Chocobo I have the same issue with the Maelstrom version of this achievement