I have a group of 7 subjects (rats) and I would like to perform a group
analysis (mixed effects).
I have done the 1st level analysis (fixed effects) for each subject and
I have two con_001 and con_002 images, wich are respectively the
contrast image for a positive effect (activation) and for a negative
effect (deactivation) of one condition (current stimulation) .
Then, I have done a one-sample-t-test : I feed all the con_001 of each
subject into the 2nd level analysis , then I entered a T contrast 
and SPM displayed the thresholded T-statistic image. But when I entered
a F contrast , I have got this error:
??? Inf computed by model function, fitting cannot continue.
Try using or tightening upper and lower bounds on coefficients.
Based on the procedure described in SPM8 manuel concerning the "face
group data", It is mentionned that I have to enter a F contrast.
I am confused by this and I have some questions:
(1) which contrast should I enter, F or T contrast? and what is the
differenece between them?
(2) Is the one-sample-t-test, the appropriate one to run mixed effects
(3) Do I have to run two separate "one-sample-t-test" for
positive(activation) and negative-deactivation) effects?
Thank you for your help.