Phew, found the problem. Turns out that when I added a parameter definition to the subreport, I put the name of the parameter, without any other treatment, as the value. I had wondered about the name Value for that field, but that's what I did. I had also tried saying @RP1 (RP1 being the name of the mail report's parameter that I wanted tied to the subreport's parameter), thinking that would definitely say it was a variable, but both of these had been giving me that "Error: Subreport could not be shown" message. I went back into the subreport object's properties window, and clicked on Parameters again, and then clicked on the fx (function) button. I went to Category/Parameters and then double-clicked the RP1 parameter I wanted, and in the "Set exporession for: Value" box, it showed "=Parameters!RP1.Value", and when I clicked OK, the Value field then had the text [@RP1], including the square brackets, which I take it means to use @RP1 as a variable and not a string. Without the square brackets it was being treated as a string, and therefore not being passed by value. Just writing this in case some other newbie comes along and misses this key point as well. Not sure why I didn't see any references to this misunderstanding in other posts.