The NAs are coming from the fact that each 'Sample' (which I assume is a unique identifier for a sample) is not actually a number and so there's no correlation.
However, I strongly recommend altering your approach here and using a binary matrix for these correlations. That is, assuming your CData looks something like
treatment replicate
1 1
1 2
1 3
2 1
2 2
... ...
8 2
8 3
then using cdata.bin <- model.matrix(~ treatment + 0, data=CData) will give you the appropriate structure for the module trait heatmap. Right now "green" is telling you the module is "up in early groups" and red is telling you the module is "up in late groups", but you can't pinpoint specific ones. Breaking this all out into a 24x8 matrix (which model.matrix does for you) will give you far more detail.