error with real time data acquisition toolbox and simulink

hello,

I'm running DAQ in real time with matlab simulink using analog input block, always the model is running for few seconds then stop and show the following error msg!

Error reported by S-function 'sdaqaiss' in Analog Input (Single Sample)': This acquisition has already been armed and started.

what does it mean? urgent help please

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency