If you are getting a bus error on the read.otu command and are using a version earlier than 1.6, the problem is most likely due to a discrepancy between your list and group files. With such large files these types of errors can be extremely hard to spot, so in version 1.6 we added a feature to report the differences to you so you can easily find a missing name from either file. Thanks to all the users who helped us track this one down!