Hello Ken, The reason you are encountering this is error is because 'chr11_random' does not exist in hg16. The different assemblies do not always have the same sequence fragments. You can click the 'sequences' link on the Gateway page of each assembly to see the names of all the sequences for that assembly (http://genome.ucsc.edu/cgi-bin/hgGateway).
I would also like to let you know that our mailing list does not handle attachments well, so if you have further inquiries, it might be best to copy the text of the error into a standard message. I hope this helps you get things straightened out. Please contact us again if you have further inquiries. Best Antonio Coelho UCSC Genome Bioinformatics Group _______________________________________________ Genome maillist - [email protected] https://lists.soe.ucsc.edu/mailman/listinfo/genome
