実は原因はExcel 64ビットでした。
Makro.xlm ワークシートには、次の関数定義が含まれていました。
Private Declare Function FindFirstFile Lib "kernel32.dll" Alias "FindFirstFileA" ( _
ByVal lpFileName As String, _
ByRef lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function FindNextFile Lib "kernel32.dll" Alias "FindNextFileA" ( _
ByVal hFindFile As Long, _
ByRef lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function FindClose Lib "kernel32.dll" ( _
ByVal hFindFile As Long) As Long
Private Declare Function FileTimeToLocalFileTime Lib "kernel32.dll" ( _
ByRef lpFileTime As FILETIME, _
ByRef lpLocalFileTime As FILETIME) As Long
Private Declare Function FileTimeToSystemTime Lib "kernel32.dll" ( _
ByRef lpFileTime As FILETIME, _
ByRef lpSystemTime As SYSTEMTIME) As Long
それらをptrsafeに変更しました:
Private Declare PtrSafe Function FindFirstFile Lib "kernel32.dll" Alias "FindFirstFileA" ( _
ByVal lpFileName As String, _
ByRef lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare PtrSafe Function FindNextFile Lib "kernel32.dll" Alias "FindNextFileA" ( _
ByVal hFindFile As Long, _
ByRef lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare PtrSafe Function FindClose Lib "kernel32.dll" ( _
ByVal hFindFile As Long) As Long
Private Declare PtrSafe Function FileTimeToLocalFileTime Lib "kernel32.dll" ( _
ByRef lpFileTime As FILETIME, _
ByRef lpLocalFileTime As FILETIME) As Long
Private Declare PtrSafe Function FileTimeToSystemTime Lib "kernel32.dll" ( _
ByRef lpFileTime As FILETIME, _
ByRef lpSystemTime As SYSTEMTIME) As Long
今ではうまくいくようです。