Warning: possibly incomplete model

Hello everyone, 

I am wanting to test whether the association between trait and functional connectivity is different between my two groups and have set up the group comparison like so:

"GroupA", "GroupB", "Trait_groupA", and "Trait_groupB" second-level covariates, contrast [0 0 1 -1]

However, during my second level analyses, I have been receiving an error that says "Warning: possibly incorrect model: no constant term modeled (suggestion: add AllSubjects term to selected subject-effects list)." 
I have attached a screenshot of this below.

Any suggestions as to how to fix this error? 

Also - I was wondering if it is possible to export the design matrix to a .txt file? 

Thank you! 
Leyla