HP 48GX IFT Error: Too Few Arguments

[MNH]

Program: CURVE

\<< { 6 7 8 9 } CF {
{ "Δ"
\<< 'D' STO 6 SF 9 FS? CALC IFT 9 SF \>> }
{ "R"
\<< 'R' STO 7 SF 9 FS? CALC IFT 9 SF \>> }
{ "T"
\<< 'T' STO 8 SF 9 FS? CALC IFT 9 SF \>> }
} TMENU
\>>

@ D is for delta (central angle).
@ R is for radius.
@ T is for tangent length.
@ If user flag 9 is set, program executes CALC and the 2 selected curve
parts are used to calculate the remaining 6 parts.

Input example:

30, press menu key below Δ

Output:

@ Executes CALC
@ Displays
IFT Error:
Too Few Arguments
@ 1: 0

Upon entering the first curve part, the program should not execute CALC because user flag 9 is clear; the program returns 0 to stack level 1. Why "IFT Error: Too Few Arguments?" I'm following the IFT command syntax. What am I missing?