URGENT - have code that only works for 32 bit-need 64 too!

If it will only be run on 2010 or later, you can just use:

Declare PtrSafe Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" (ByVal hwnd As LongPtr, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As LongPtr

If your code stores the return value in a variable, make sure to declare that variable as LongPtr not Long.