This is a very misleading error that is sometimes generated by InDesign during export.

png error message

It doesn't have anything to do with memory.

The issue is that in5 is trying to export a page item from InDesign, but the item doesn't generate any visible pixels (like a line that has no stroke). in5 successfully skips most items that won't render, but occasionally one gets through the cracks and you may see this error during export.

This error is completely harmless and you safely can ignore it. Simply click OK and the export will continue processing. 

If you want to report it, you can send your document to us and we'll improve the code to avoid generating this error in this particular circumstance going forward.