David,

You should just put the code inside the class' Error() method. Any errors that occur within the methods of the class will be cause that method to execute.

define class mydll as ...
function Error( nError, cMethod, nLine )
strtofile( dtoc( datetime() ) + " error:" + transform( nError ) + " in " + ;
   cMethod + " at line " + transform( nLine ) + chr(13) + chr(10), "c:\errorlog.txt", .t. )
endfuc
enddefine

>I have a VFP8 MTDLL. Inside are various functions. One of the functions is an ErrorProc to handle errors. When I attempt to set ON ERROR DO ErrorProc or ON ERROR This.ErrorProc or ON ERROR DO This.ErrorProc I get an Error (??).
>
>How does one set up an Error handler from within a COM environment?