#define FAN_PIN            -1

#define FAN_PIN            4

UPDATE - 02/18/2014
Ok, for anyone else who wants to rip there hair out if they too want to add a gcode controlled fan to their Panelolou 2 + Solidoodle setup, but can't seem to get it work. Make the following changes. You want to use transistor 2 on your Sanguino adapter board.

Transistor 1 will not work until i2c is supported by firmware. Which I think it is already, but I haven't confirmed it. If it is I believe it's simply a matter of soldering a few jumpers together on the Sanguino adapter board that comes with the Panelolou 2. 

Anyhow code changes as follow to the Pins.h file in the Marlin Soliforum Community firmware.  What I changed the code too is anything that is red below.

/****************************************************************************************
* Sanguinololu pin assignment
*
****************************************************************************************/
#if MOTHERBOARD == 64
#define STB
#endif
#if MOTHERBOARD == 63 || MOTHERBOARD == 66
#define MELZI
#endif
#if MOTHERBOARD == 65
#define AZTEEG_X1
#endif
#if MOTHERBOARD == 62 || MOTHERBOARD == 63 || MOTHERBOARD == 64 || MOTHERBOARD == 65 || MOTHERBOARD == 66
#undef MOTHERBOARD
#define MOTHERBOARD 6
#define SANGUINOLOLU_V_1_2
#endif
#if MOTHERBOARD == 6
#define KNOWN_BOARD 1
#ifndef __AVR_ATmega644P__
#ifndef __AVR_ATmega1284P__
#error Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu.
#endif
#endif

#define X_STEP_PIN         15
#define X_DIR_PIN          21
#define X_STOP_PIN         18

#define Y_STEP_PIN         22
#define Y_DIR_PIN          23
#define Y_STOP_PIN         19

#define Z_STEP_PIN         3
#define Z_DIR_PIN          2
#define Z_STOP_PIN         20

#define E0_STEP_PIN         1
#define E0_DIR_PIN          0

#define LED_PIN            -1

#define FAN_PIN            28 //Needs to be pin 28 to use Transistor 2 on panelolou 2 Sanguino adapter board.
#if FAN_PIN == 12 || FAN_PIN ==13
  #define FAN_SOFT_PWM
#endif

#ifdef MELZI
#define LED_PIN            27 /* On some broken versions of the Sanguino libraries the pin definitions are wrong, which then needs LED_PIN as pin 28. But you better upgrade your Sanguino libraries! See #368. */
#define FAN_PIN            28 // Works for Panelolu2 too, should be 28 for Transistor 2 use and non broken Sanguino library.
#endif

#ifdef STB
#define FAN_PIN            4
    //  Uncomment this if you have the first generation (V1.10) of STBs board
#define LCD_PIN_BL         17 // LCD backlight LED
#endif

#ifdef AZTEEG_X1
#define FAN_PIN            4
#endif

#define PS_ON_PIN          -1
#define KILL_PIN           -1

#define HEATER_0_PIN       13 // (extruder)
#define HEATER_1_PIN       -1
#define HEATER_2_PIN       -1

#ifdef SANGUINOLOLU_V_1_2

#define HEATER_BED_PIN     12 // (bed)
#define X_ENABLE_PIN       14
#define Y_ENABLE_PIN       14
#define Z_ENABLE_PIN       26
#define E0_ENABLE_PIN      14

#ifdef LCD_I2C_PANELOLU2
   #define FAN_PIN          28 // Uses Transistor1 (PWM) on Panelolu2's Sanguino Adapter Board to drive the fan, change to pin 28 to use transistor 2.
#endif

#else

#define HEATER_BED_PIN      14  // (bed)
#define X_ENABLE_PIN       -1
#define Y_ENABLE_PIN       -1
#define Z_ENABLE_PIN       -1
#define E0_ENABLE_PIN      -1

#endif

#define TEMP_0_PIN          7   // MUST USE ANALOG INPUT NUMBERING NOT DIGITAL OUTPUT NUMBERING!!!!!!!!! (pin 33 extruder)
#define TEMP_1_PIN         -1
#define TEMP_2_PIN         -1
#define TEMP_BED_PIN        6   // MUST USE ANALOG INPUT NUMBERING NOT DIGITAL OUTPUT NUMBERING!!!!!!!!! (pin 34 bed)
#define SDPOWER            -1
#define SDSS               31

There you go, hope this helps anyone with this unique problem! I'll be seeing if I can get access to both my transistors by checking into what's needed for i2c support with my setup. I'll post an update if I figure anything else out.