Stata Tech Support has verified that there is a bug in version 16.1 import sas. If a SAS dataset (sas7bdat) has observations containing NaN (not a number) fields, they are not mapped into Stata missing values, but retained as such. The data import without any errors, but use of a command like codebook will cause Stata to enter an infinite loop, from which a force quit is the only solution. It is likely that any command that sorts the data on a variable containing NaNs will cause the same problem.