Unable to partition my HD using Bootcamp Assistant

[SeHou]

Hello, i`m trying to install Win 8.1 on my Mac Pro, i have a 3TB HD with a single partition. When i try to start Bootcamp Assistant it spits out: "The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows"

This is my partition map:

$ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 3.0 TB disk0s2

$ sudo gpt -vv -r show /dev/disk0
Password:
gpt show: /dev/disk0: mediasize=3000592982016; sectorsize=512; blocks=5860533168
gpt show: /dev/disk0: PMBR at sector 0
gpt show: /dev/disk0: Pri GPT at sector 1
gpt show: /dev/disk0: Sec GPT at sector 5860533167
start size index contents
0 1 PMBR
1 1 Pri GPT header
2 32 Pri GPT table
34 6
40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
409640 5859861344 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
5860270984 262151
5860533135 32 Sec GPT table
5860533167 1 Sec GPT header

Any idea? Thanks!