Collection size exceeds maximum size of 1,000
This error usually occurs when you have more than 1000 objects in your Salesforce org. The Visualforce method cannot query more than 1,000 objects for the Master Object dropdown.

Composer for Salesforce 
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This error usually occurs when you have more than 1000 objects in your Salesforce org. The Visualforce method cannot query more than 1,000 objects for the Master Object dropdown.
If you're creating a lot of solution records, change the Page Layout to rearrange the sequence of the Master Object Type field for better usability.
