can you see if this is it?
=iif(Fields!ActingFor.Value = "", "Regards", "Signed for and on behalf of " & Fields!ActingFor.Value & " ") &
IIF(Parameters!AcceptNotice.value = True,"(as " & Parameters!ActingAs.Value & " of " & Fields!TRUST_DESCRIPTION.Value & ")","")
If Fields!ActingFor.Value = ""
yields "Regards"
ELSE
yields "Signed for and on behalf of " & Fields!ActingFor.Value & " ") &
If Parameters!AcceptNotice.value = True
appends "(as " & Parameters!ActingAs.Value & " of " & Fields!TRUST_DESCRIPTION.Value & ")"
to the "Signed..." string above.
If I am wrong on the logic please explain your desired results.
HTH,
Chris