mplus求助，最后的变量识别不出来， Unknown variable(s) in a BY statement: DD-经管之家官网！

求大神帮忙！mplus小白一个，做毕业论文，一个链式中介模型mplus跑出来的结果是
*** ERROR in MODEL commandUnknown variable(s) in a BY statement:D1
代码如下：
DATA: FILE IS shuju22.dat;
VARIABLE:
NAMES ARE A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 B1 B2 B3 B4 B5 B6 C1 C2 C3 C4 D1 D2;
USEVARIABLES AREA1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 B1 B2 B3 B4 B5 B6 C1 C2 C3 C4 D1 D2;
ANALYSIS:
bootstrap=3000;
MODEL:
X by A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13;
M1 by B1 B2 B3 B4 B5 B6;
M2 by C1 C2 C3 C4;
Y by D1 D2;
Y ON X(c1)
M1(b3)
M2(b2);
M2 ON X(a2)
M1(b1);
M1 ON X(a1);
MODEL CONSTRAINT:
new(h1);
h1= a1 * b3;
new(h2);
h2= a2 * b2;
new(h3);
h3= a1 * b1 * b2;
OUTPUT: STANDARDIZED SAMPSTAT MODINDICES cinterval(bootstrap);