One of the problems I've been running into with SmartSection comes from the way it pulls data related to the categories. It pulls ALL the data including the description and such to just display the category info. If you have robust category description pages, then that can be a LOT of data. Increasing the memory for the php scripts can help reduce this. I don't know if that's your problem, but it could be.
I know there are several other content modules out there that can meet this functionality, but don't yet know how they compare. If you do a look at them all, please give feedback as to what worked or didn't and why. I'll be looking for one with robust permissioning like this module among other things and support. This module has been a great tool, though.
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