@alexandra-vita    It would be extremely helpful if you show us the output from that code so we can see what you are seeing. Create a screen capture of the output and include it in your reply using the "Insert Photos" icon; do NOT attach files.     I agree that it is likely you do not have enough degrees of freedom in your data, and this happens because you have as many terms in the model as data points. But SHOW US the output. ... View more

Try removing the "=" sign after class   CLASS  treatment (ref="A") sequence (ref= "AB") period (ref= "P1") time (ref="V1");   ... View more