Hi:
As Scott recommends, if you cannot make the HTMLPANEL tagset work, then you need to open a track with Tech Support. When I run the examples, as downloadable from this page, I am able to generate side-by-side output.
http://support.sas.com/rnd/base/ods/odsmarkup/htmlpanel.html
In particular, the PANELOPT.SAS program in the ZIP file shows how to generate 3 side by side tables. Modifying that program to generate 2 tables side-by-side should work for you. If you have not been able to make PANELOPT.SAS work for you, then you should contact Tech Support.
Remember that if you are using the ODS TAGSETS.HTMLPANEL destination, then you would NOT have 2 ODS HTML CLOSE statements in your code....as shown in the examples for invoking the HTMLPANEL destination.
cynthia