måske dette ..?
Change the local security policy through the Local Security Policy application or via the Registry.
To change the policy with the policy editor, open the Local Security Policy application under Administrative Tools in the Control Panel.
Under Local Policies->Security Options set the entry for "Restrict CD-ROM access to locally logged-on user only" to Disabled.
Alternately, you can modify the setting in the Registry. Change the value for the key allocatecdroms under the branch HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\WinLogon to 0.
kilde..>
http://support.wolfram.com/mathematica/systems/windows/general/install_error1311.html