NIST random test suite choosing bitstream length and count
Look for the document "NIST Randomness Testing SP800-22b.pdf" (or more recent updates if available) in the NIST website.

My guess is that your sequences are way too short (32 bits long) and no kind of statistical convergence can be expected to occur, which is necessary for the test to work. I presume this may be the reason why you get the error message.

The section "sequence length", p.102 in the NIST document states:


  The determination as to how long sequences should be taken for the
  purposes of statistical testing is difficult to address. If one
  examines the FIPS 140-1 statistical tests, it is evident that
  sequences should be about 20,000 bits long.


Coupled with this, you have 1 million such outputs. Depending on the conditions of how these outputs were obtained, you may want to concatenate them into longer outputs, in some principled manner.