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The only version of SmartSection that requires SmartObjects is v2.14beta.
If you haven't done so already, I suggest that you go over to
http://www.smartfactory.ca/ and report this bug on their Forums.
In the meantime, use SmartSection 2.13Final as it works fine on XOOPS 2.0.18.1 and php5; you will be able to update to 2.14 when the final version is released with, hopefully, your bug corrected.
Okay, you won't have rating enabled but any articles that write in SmartSection will be retained after upgrade.
Sorry, but I personally can't be of more help.