the QD data cann't be read by S7Prosim

I had alreadyconnected PLCSIM with S7Prosim in VB 6.0, but when I try to read Output Image, I found that QDxxx cann't be read at all, the value was always 0 as i tried many times, I don't know why, plaese help me. thank you very much!

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Code：

PrivateSubReadQImageCMD_Click()

DimrQ

S7ProSim1.ReadOutputImage0,1,S7_Byte,rQ

LogText.Text=Now&":QB0="&Hex(rQ(0))&vbCrLf&LogText.Text

S7ProSim1.ReadOutputImage0,1,S7_Word,rQ

LogText.Text=Now&":QW0="&Hex(rQ(0))&vbCrLf&LogText.Text

S7ProSim1.ReadOutputImage0,1,S7_DoubleWord,rQ

LogText.Text=Now&":QD0="&Hex(rQ(0))&vbCrLf&LogText.Text

S7ProSim1.ReadOutputPoint0,1,S7_Byte,rQ

LogText.Text=Now&":QB0="&Hex(rQ)&vbCrLf&LogText.Text

S7ProSim1.ReadOutputPoint0,1,S7_Word,rQ

LogText.Text=Now&":QW0="&Hex(rQ)&vbCrLf&LogText.Text

S7ProSim1.ReadOutputPoint0,1,S7_DoubleWord,rQ

LogText.Text=Now&":QD0="&Hex(rQ)&vbCrLf&LogText.Text

EndSub

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results：

2009-10-720:58:55:QD0=0

2009-10-720:58:55:QW0=8700

2009-10-720:58:55:QB0=87

2009-10-720:58:55:QD0=0

2009-10-720:58:55:QW0=8700

2009-10-720:58:55:QB0=87