Those warnings about FDR simply indicate that the associated statistical evidence is weak in terms of the false discovery rate. In other words, that is just how much information your data could provide based on the current model.
You can also ignore the following message (a numerical indicator for some statistical construct at some voxel(s)).
> Warning message:
> In summary.Anova.mlm(object$Anova, multivariate = FALSE) : HF eps > 1 treated as 1
Gang