the serial read didnot complete within the specified timeout period

I have been using a Cobra-SRC and a frame grabber PCIe-1433 of NI for a while. I use LABVIEW to make Cobra-SRC work and used MATLAB to read data from PCIe-1433. Before they all ran well but now, when grabbing, it showed a dialog in LABVIEW:"IMAQ error: the serial read didnot complete within the specified timeout period". And an error occurs in MATLAB: "ni: cannot detect recognizable video source". I'm so confused that I did not change anything in MATLAB and LABVIEW. Could someone answer me this question???? Thank you in advance.