*SOLVED* Overflow when dividing

ok...
im making a paint program, and when the user is going to draw a straight line, he has to do as in mspaint: hold down shift....
the problem is when the program is going to calculate the M value and the K value of the line...

here's a bit of the code:

If Shift = 1 Then
KValue = (Y - StartY) / (X - StartX)
MValue = Y - X * KValue
End If

but it cant do the division!! it gives me the overflow error!
why?

make sure that k and m are not defined as bytes (which can't be more then 255 or less then 0 (I really really hope u knew that)) or that ur not dividing by 0, make sure x - xstart doesnt = 0 so

if not x - xstart = 0 then
KValue = (Y - StartY) / (X - StartX)
else
kvalue = 0 'or whatever will work right...
end if
MValue = Y - X * KValue