Thanks for your reply, I now have a better view on what you are trying to achieve.
Regarding the error you are having, it is very difficult to investigate this as we would require more detailed information which is not possible in this forum thread.
I therefor suggest, should you want to persue this, to open a support ticket so that that we can have a look at it in more details.
Now, based on your explanation I have the impression that you are using an older version of Sitefinity.
From Sitefinity version 7.0 and on, you can include related content to dynamic modules, built-in modules, and pages.
All this is implemented out of the box and you can relate content to any other content, thus creating complex architectures of structured data that is easily manageable. You can create one-to-one or one-to-many relations between different items. Sitefinity makes it easy to display all related items on the frontend.
Therefor it would be better to think about upgrading to a newer version.
Here is a direct link to the complete documentation on this:
Content relations: Related data
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