Please create a new mount directtory as a test on AIX server and try mounting on it.
Still does not work, export with IP adress of AIX server , mount it on the new mount point and try.
exportfs -u /vol/vol_name <<unexport current
exportfs -io rw,root=IP_addr_AIX /vol/vol_name <<export with minimal option
Also post the error message logged in /etc/message file, if any.