Pin designators must match exactly:
- Open the schematic symbol and confirm every pin has a unique designator (no duplicates, no blanks).
- Open the linked PCB footprint and confirm pad designators match the symbol’s pins (1 ↔ 1, A ↔ A). Mismatches cause pin errors.
- Cross-check pin assignments against the datasheet; verify the symbol’s pin names match the device pins exactly (avoid swapped or aliased names).
Annotation and Unique IDs:
- If this appears during ECO, reset IDs to clear corruption: Tools -> Reset Component Unique IDs (schematic and PCB), then update PCB from schematic again.
- Run Annotate to ensure all designators are unique before updating.