Levels of the repeated effect

[Wienta Diarsvitri]

Hello all,

I have pre test & post test data on knowledge, attitude & behavior intent from 16 schools. 8 schools are in intervention group & 8 are in control group. There are at least 60 students from each school. I am trying to use LMM repeated measurement. Time is in 2 level. However, every time I put time as a repeated variable, there is a message appear: the levels of the repeated effect are not different for each observation within a repeated subject. This command is not executed. What does it mean and why does it happen?

Thank you very much for all your help.

Sincerely,

Wienta