Error = Your forms cache is probably corrupt
I tried this reg edit
Outlook 2016:
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Office\16.0\Outlook\Security
DWORD: DisableCustomFormItemScript
Value: 0 (to enable)
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Office\16.0\Outlook\Forms\TrustedFormScriptList
REG_SZ: IPM.Note.AfterMail
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\16.0\Outlook\Security
DWORD: DisableCustomFormItemScript
Value: 0 (to enable)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\16.0\Outlook\Forms\TrustedFormScriptList
REG_SZ: IPM.Note.AfterMail
Value: (leave blank)
Any ideas?