The above post appears to be for Diskeeper 8 (but it could work for 9 I would guess). However, after doing some testing, it appears that it's Windows Firewall that is causing the issue. So here is the Registry key to add Diskeeper to the ok list...
CODE
[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List]
"C:\\Program Files\\Executive Software\\Diskeeper\\Diskeeper.exe"="C:\\Program Files\\Executive Software\\Diskeeper\\Diskeeper.exe:*:Enabled:DISKEEPER.EXE"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List]
"C:\\Program Files\\Executive Software\\Diskeeper\\Diskeeper.exe"="C:\\Program Files\\Executive Software\\Diskeeper\\Diskeeper.exe:*:Enabled:DISKEEPER.EXE"