Salve,
ho visto i link descritti, ho modificato la chiave di registro e dopo aver aperto il file .xlsm e contemporaneamente il file indicato nella parte inferiore della foto, appare il pop seguente.

Il registro modificato è il seguente:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security]
"VBAWarnings"=dword:00000003
"DisableAllAddins"=dword:00000000
"NoTBPromptUnsignedAddin"=dword:00000000
"RequireAddinSig"=dword:00000000
"AccessVBOM"=dword:00000001
"ExtensionHardening"=dword:00000000
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations]
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location0]
"AllowSubFolders"=dword:00000001
"Path"="C:\Program Files\Microsoft Office\Office12\XLSTART\"
"Description"="3"
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location1]
"Path"=hex(2):25,00,41,00,50,00,50,00,44,00,41,00,54,00,41,00,25,00,5c,00,4d,\
00,69,00,63,00,72,00,6f,00,73,00,6f,00,66,00,74,00,5c,00,45,00,78,00,63,00,\
65,00,6c,00,5c,00,58,00,4c,00,53,00,54,00,41,00,52,00,54,00,00,00
"Description"="4"
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location2]
"Path"=hex(2):25,00,41,00,50,00,50,00,44,00,41,00,54,00,41,00,25,00,5c,00,4d,\
00,69,00,63,00,72,00,6f,00,73,00,6f,00,66,00,74,00,5c,00,54,00,65,00,6d,00,\
70,00,6c,00,61,00,74,00,65,00,73,00,00,00
"Description"="5"
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location3]
"AllowSubFolders"=dword:00000001
"Path"="C:\Program Files\Microsoft Office\Templates\"
"Description"="6"
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location4]
"AllowSubFolders"=dword:00000001
"Path"="C:\Program Files\Microsoft Office\Office12\STARTUP\"
"Description"="7"
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\Trusted Locations\Location5]
"AllowSubFolders"=dword:00000001
"Path"="C:\Program Files\Microsoft Office\Office12\Library\"
"Description"="12"
Grazie