SPSS v21 - MANCOVA post-hoc test - post-hoc box grayed out

Hi everyone,

I'm looking to run a Tukey post-hoc test in GLM-->Multivariate with covariates (MANCOVA).

When I add covariates I can no longer select "post-hoc" - the box is grayed out. Also, I can't click "compare main effects" in the options tab.

Why is this? I have seen a thread similar to this with ANCOVAs, but this was solved by selecting options-->compare main effects.

Any help is appreciated, either technical or theoretical.