I am running a 2 level analysis with students clustered within schools. I get an error stating that there is within cluster variability for L2 predictors in certain clusters; the error message identifies one of these clusters. However, when I check the data, this is not the case. For instance, the error message says that cluster 4301 has within cluster variability on a L2 predictor, principal's years of experience. However, when I check the data for that cluster, all of the observations for that cluster are identical. I have checked and double checked to ensure that variable names are accurate. It occurred to me that this might be an issue with missing data that is coded as a blank cell, so I replaced all blank cells with negative numbers. However, none of these solutions has solved the issue, and I am not sure what else to try. Thank you for your help!