LabView: Error -50103; operation could not be completed as specified

I am receiving the Error -50103 "specified resource is reserved" when I try to write multiple simultaneous waveforms with a phase shift to multiple analog output channels. Why do I get the error? How do I prevent this?

Error -50103 occurred at DAQmx Write (Analog DBL 1Chan 1Samp). VI: 1
Possible reason(s):
The specified resource is reserved. The operation could not be completed as specified.
Task Name: _unnamedTask<3>
