Recently I came across an error that I have not seen before. It seemed this error was only happening on one item. This might be something you never come across or eventually will. Either way there is a good way to prevent it.
The error I saw was below. This happened when you tried to add a datasource to a specific rendering. Not the most descriptive, but it looks like Sitecore returns a big query string of an item’s children.
After examining the rendering I noticed the query that was used in the datasouce location would actually query all children.
The easy fix was to create a components folder and keep the datasource items in there. Then the query could be changed to the following which would only look for that folder. No more errors. Of course, you can expand on the query such as adding the specific templates of the datasource.