Each report has an error event showing the processing item that is source of the exception.
in this case, the problem can be related to images loaded in reports or styles. Please test removing images (background images and/or PictureBox items) one by one. Remove in the same way styles, until you detect the one causing the problem.
Test also to run preview without loading data in reports.
If you need further help, please post the code for generating the main and sub reports, which will allow us to create local test.
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