Hi @NN,
We have customers running this on AIX. You don't mention the version of PostgreSQL you are using or the maintenance level of SAS (M<and some number>). This information is important in diagnosing the issue.
Make sure that you are using a supported version of PostgreSQL. Here is a screenshot from the SAS Systems Requirements for SAS 9.4 on AIX. Your best bet may be to contact tech support.
UPDATE: SAS 9.4M6 requires a Hot Fix (H3J001) to be installed to get access to use BULKUNLOAD=.
This SAS Communities article may be of assistance - An Insider's Guide to SAS and Database Support Information.
Best wishes,
Jeff
"Who used to be the product manager for SAS/ACCESS"