Version 1.5.1 is a maintenance update as it appears there was a “fat-finger” error introduced in the Desk Mess Mirrored version 1.5 that causes the sidebar widget areas to become unavailable.
This release was uploaded to WordPress.org on Apr 23, 2010 but has not been approved as I suspect the WordPress 3.0 bug sprint has pulled all their resources into that endeavor. Please be patient, once this version (1.5.1) is available the issue with the sidebars will be resolved.
NB: Version 1.5.1 of Desk Mess Mirrored is now live at <http://wordpress.org/extend/themes/desk-mess-mirrored> as of Apr 28, 2010, unfortuantely the automatic update is not currently working. Please download the theme and see below.
Once downloaded, you can un-zip the file and upload the contents to overwrite the existing theme via FTP; or, you can change to the default theme, delete the existing Desk Mess Mirrored (version 1.5) theme, upload the zip file under Appearance | Themes | Add New; then, activate the theme.