First, see my last two posts about connecting the dots:
After that, you'll probably still have issues. If you see a "Too many bytes for comparator" it most likely means that you have a mistmatch between your PRIMARY KEY declaration in your CQL CREATE TABLE statement, and the composite you are using in Astyanax.
You have to be really careful that all of the components in the primary key are declared in your class *in order* and that all fields in your class are part of your primary key. Otherwise, when Cassandra goes to compare two column keys/names, it will generate the bytes for that column name (from all the components) and it will end up with too many or too few. (Hence the error you are seeing)
If you have too many, there is a good chance that you have a field declared in your annotated composite class, that is not part of your primary key declaration.
Hopefully that helps. If you want the underlying theory/reasoning, see:
If it still takes you a while to get sorted out, accessing a CQL table from a thrift-based client, no worries... you are in good company: