Hope someone can help me with the following problem/question I encounter.

I'm working with a monthly time-serie consisting of 36 data points (i know 50 is the rule of thumb). Spss expert modeler chose Winter's multiplicative model, which is fine with me because I know how such a model works. Stationary R-Square is .72, also fine.

Now the problem;

- My Ljung-Box Q statistic is significant (p= .001) indicating a problem with my model; it can't explain a part in my model or there is autocorrelation left if i'm right (?).

- I thought, well let's first look if the residuals are non-normal, but Shapiro-Wilk statistic is non-significant (p=.65), which i didn't expect.

Question 1: What is the relation between Ljung-Box Q statistic and the normality of my residuals?

After asking myself that question, I plotted the residual acf and pacf which resulted in the following graph, showing values out of the boundaries.

Question 2: I suppose this causes my Ljung-Box Q statistic to be significant, but how can I solve this?

Hope someone can help me, I got lost..