If the shortest distance between the lines $\dfrac{x-4}{2}=\dfrac{y+1}{3}=\dfrac{z-\lambda}{2}$ and $\dfrac{x-2}{1}=\dfrac{y+1}{4}=\dfrac{z-2}{-3}$ is $\dfrac{6}{\sqrt{5}}$, then the sum of all possible values of $\lambda$ is: