Yes we will probably need some code, but don't paste it all! Just the relevant bits - the method the error occurs in, say.
Having said that, most of the time it is pretty simple to work out where the problem:
The error says "Object reference not set to an instance of an object"
That means that somewhere you are using an object and trying to work with a feild, method, or property, but the object itself is not set.
The problem will be something along the lines of
myVariable.myMethod
or
myArray[index].myMethod
The error message (and the exception) will tell you which line it is occurring on. Look at it in the debugger and follow the variables until you find the problem.
You may find it helps to break everything out into separate variables on separate lines until it is just one tiny bit of code per line.
MyArray[myIndex].myMethod().myProperty = 0;
becomes:
MyObject my1 = MyArray[myIndex];
MyOtherObject my2 = my1.myMethod();
MyThirdObject my3 = my2.myProperty;
my3 = 0;
Try it - it is a skill well worth developing yourself!