Hi Boris, 

I thin the error is in this line

mismatched number of scans and covariate datapoints ([2 1] vs. [800 16])

You seem to have loaded only two functional files, but your 16 covariates are 800 TR long.

This mismatch causes the error. Try reloading your functional files, and take care to add all the volumes you need.

Kind regards

Eugenio