[C#] Getting a NullReferenceException on a Timer method.

Full code for ease of viewing: https://gist.github.com/anonymous/7c0e645976add17e49a5[1]

I'm creating a Pacman game and I have ran into a bit of a problem. Before we start, I should explain how the map is created. Within the Cell.cs class there is a case statement which creates lines/dots and them assigns to each case. Within a text file I have arranged these cases into a pattern that takes the form of a pacman map.

The problem I am having is with a timer statement (line 243 of Gameboard class / line 4 in code snippet) throwing a NullReferenceException.

if (pacman.pacmanFacing == 0)         {               //check for cells type o, d and p                            if (cells[yPos + 1, xPos].CellType == 'o' || cells[yPos + 1, xPos].CellType == 'd' || cells[yPos + 1, xPos].CellType == 'p') 

I originally had these if else statements in a "Gameboard_KeyDown" method (Gameboard is the main form). They worked fine while in that method.

But I have to move them to a Timer method in order to animate the Pacman character. 16 images as found in the MovingPacman.cs file separated into 4 images for each direction are for this purpose. They are called by these lines of code:

           pacman.currentMouthPosition += 1;                     if (pacman.currentMouthPosition > 3) pacman.currentMouthPosition = 0; 

I should also mention that when I set the timer to 10000 milliseconds it does not throw an error while its default 100 does. However, moving the pacman does still not work in this forced state.