Interesting. When I go to Confluence admin to disable/enable, I find the panel macro as part of the Basic Macros plug in and all the modules therein are disabled which is probably what is causing the error message.
Poking around a little on Atlassian's site, I found that the Basic Macros plug in is not available for On-Demand https://marketplace.atlassian.com/plugins/confluence.macros.basic#support (Click the OnDemand tab under Pricing OverView).
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