Maybe your error is due to a wrong indication of trigger channel with respect to acquired channels list.
I quote for you some help taken from a LV example (Cont Acq&Graph (buffered) Hard A-Trig.vi):
"...With E Series devices, if your analog trigger signal is connected to one of the analog input channels, that channel must be first in the scan list of channels. If you are using named channels, the trigger channel must be the first channel in the actual hardware channel order, which may or may not be the first channel in the channel string control. This restriction does not apply if you connect the analog trigger signal to PFI0..."
Roberto