Welcome to the forum for MLwiN users. Feel free to post your question about MLwiN software here. The Centre for Multilevel Modelling take no responsibility for the accuracy of these posts, we are unable to monitor them closely. Do go ahead and post your question and thank you in advance if you find the time to post any answers!
It sounds like you may have made an error when filling in the dialogue to calculate this. I suggest that you look at page 127 of the MLwiN user guide (http://www.bristol.ac.uk/cmm/media/soft ... al-web.pdf) which provides a worked example.
I am not currently aware of any bugs related to this. Looking at the screenshot you provided is appears that you have not specified the test that you want to perform. To do this you need to change some of the zeros to match the required test. The inputs all being zero would match up with the error message that you are receiving.