Theme won't unzip

I just did a brand new, fresh install of WP 3.1.2 and the first theme I wanted to install was Blogs-MU Theme.

Unfortunately, upon submitting the .zip file via the "upload theme" function, the process stops at the "Unpacking the package" step, and results in an "incompatible archive" error.

Another WPMUdev theme has been uploaded and installed using this process, with no problems.

Any suggestions?