A downloaded binary complains "libresolv.so.2: can't open file"

Because of various security problems, a new version of BIND was
released as a Solaris patch. This patch wasn't binary compatible, so
a new resolver library version needed to be made.

The binary you downloaded was build on a system with the patch
installed, your system lacks the patch or is running a release that
is too old. The patch is available for Solaris 2.3 and up and is
part of the recommended patch set.