Yo tenía el mismo problema y esta es la solución que me dieron desde IBM, funciona !!
Is it on the draft folder you see the error: Not a sub or function name: MARKMESSAGEFORFOLLOWUP?
I also wonder if you use Spanish mail template. And is it standard one?
I've checked further and you might have the same issue as SPR # RREN9JXEJC( Two "Shared Actions" Entries In Standard 9.0.1 Mail Template).
You may open the template in Designer client, and check if there're duplicate "Shared Actions" for Spanish. The workaround is to delete the empty one (without the twiste).
Please make a backup of the template before making such change. Then replace the template with this modified one. Then verify the issue.
Se ha de borrar la que no tiene el desplegable.