Struggling with missing values for basket data with apriori

I know that this has been asked before (from searching the archive) but I can also see that the WEKA software may have changed; I have tried this with 3-6-1 and 3-7.

I have some basket data (1300 instances and 300 attributes) and I have tried using ? to represent unknown values with no luck - my 2G Mac crashes (both versions of WEKA) even when I edit down the number of instances to 300 with 200 attributes. I have tried representing the true values as T, 1 and TRUE and get the same crashes.

I want to check that what is happening is what others experience. WEKA will not let me use APRIORI but filtered apriori instead (because I assume of the missing values).

Any help gratefully received.

Jonathan