This issue is a bug in the R2008a installer on Linux/Solaris. As a workaround, you can associate your MathWorks account to the new license from the License Center here:
Once you are in your account, click on the Add license button in the upper right. You can then provide the Activation Key to associate to the license. Once associated, the license will show up and be selectable in the installer.
Alternatively, once associated you can download the File Installation Key and install manually without the Internet. To do this, see the related solution, "Can I install & activate on a computer that cannot connect to the Internet?"
