Salesforce Error: "No access to field CampaignId. Either the field was removed from the entity or access to this field was removed."

This article explains how to resolve the "No access to field CampaignId" error by granting field-level security access to the Primary Campaign Source field.

Resolution for Salesforce Classic

1. Go to Setup | Customize | Opportunity | Fields
2. Click the 'Primary Campaign Source' and then click the Field-Level Security button
3. Provide both Visible and Read access to the profile of the affected user.
4. Save your changes.

Resolution for Lightning Experience

1. Go to Setup | Object Manager | Opportunity | Fields and Relationships
2. Click the 'Primary Campaign Source' and then click the Field-Level Security button
3. Provide both Visible and Read access to the profile of the affected user.
4. Save your changes.