Thanks fo your answer, but I guess that I need to explain my case more deeply. I use nidaq 7.1. I have suvbi where a buffered continuous data acquisition is done. (ai-config, daq-occurence-config,ai-start and in a loop ai-read). after some time the user can stop acquisition (ai-clear) and start the measurement. the measurement is done in another subvi. again I have ai-config, daq-occurence-config,ai-start and in a loop ai-read for the acquisition. after a data analises the user comes back to the the first window, and so on. this "loop" is done 30 times. on the 20 loop the ai-read gives NaN, depending how big te buffer of the ai-config has been set.
