Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\DisabledCmdBarItemsList]
"TCID1"="355"
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\10.0\Outlook\DisabledCmdBarItemsList]
"TCID1"="355"
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\9.0\Outlook\DisabledCmdBarItemsList]
"TCID1"="355"

To re-enable the Reply to All button in outlook, run the following REG file:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\DisabledCmdBarItemsList]
"TCID1"=-
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\10.0\Outlook\DisabledCmdBarItemsList]
"TCID1"=-
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\9.0\Outlook\DisabledCmdBarItemsList]
"TCID1"=-

It's probably useful to save the REG file on your local disk, then add a shortcut to it in your START -> Programs -> Startup folder. You can do this from windows exploder by right clicking on the .REG file and dragging it to the start button. Hover over the start button until it opens, hover over Programs, hover over the Startup, then put this shortcut at the end of the list.

Enjoy!