The error message that sent you here lists objects where there are extra Lookup Relationship fields that shouldn't be there. If the Meeting object was on that list, it's because you added more than one Lookup Relationship connector to Pitch there in Meeting - it needs to have just one. It's also possible you added one to the Pitch object, thereby connecting Pitch it to itself (!), so that would need to be deleted if it's there. In any case, to get rid of the extras so there is just one Pitch connector and it's in Meeting, follow these instructions for each of the objects listed in the error message:

1. Click the Setup gear (upper right) and select Setup 

2. Click the Object Manager tab (not the down-arrow) and select the object you need to fix from the list in the central panel

3. Click Fields & Relationships on the lefthand vertical menu

4. Find a row that shows "Lookup(Pitch)" in the column headed DATA TYPE

5. If you're in the Meeting object and that is the only "Lookup(Pitch)" field, then don't delete it because the Meeting object needs one (but only one), but if not, then click the down-arrow on the far right of that row and select Delete

6. In the pop-up, click the blue Delete button

7. Repeat the steps above for each object listed in the error message that sent you here

8. Re-grade by using the App Launcher to open the Grader App and follow instructions to run the scoring routine again and then be sure to reload the page to see the updated error list & grade certificate