Why do I get the error "The number of samples to write per channel must be an integer multiple of the samples to write per channel increment"

[Turkill]

I have a pxi-1065 and a pxi-6552 for digital I/O. Currently I have the pxi-6552 sample clock set to 20MHz.  The digital signal is set up as a 2 channel, 24 sample signal, but when I try to generate the signal I get an the following error : "The number of samples to write per channel must be a multiple of samples to write per channel increment".  The samples to write per channel increment = 32 and the samples to write is 1. 

Thanks