Merging feature classes or shapefiles with the Merge tool returns error '001156'

Description

Merging feature classes or shapefiles with the Merge tool into a new feature class returns the error:

"001156: Failed on input OID <value>; could not write value '<value>' to output field <value>."

This error indicates ArcMap is unable to merge conflicting field types or field lengths from the selected feature classes or shapefiles to the new feature class.

Cause

During the merging process, error '001156' occurs when the feature classes or shapefiles that are selected for merging contain fields with conflicting field data types or lengths. For more information, please refer to ArcGIS Help: Understanding field properties, aliases, and table display options.

Solution or Workaround

• Feature classes:
  Modify the field type or increase the field length of the feature class in Field Properties to match the field type or length for each dataset. For more information, refer to ArcGIS Help: Modifying field properties.
• Shapefiles:
  1. Export the shapefiles to feature classes.
  2. Delete the fields with conflicting values or length with the Delete Field tool.
  3. Open the Merge tool, and select the exported feature classes as input datasets.
  
  
  4. Set the output location and run the Merge tool.
  
  

  Note:
  To add the conflicting data that was deleted into the merged feature class, create a new field and specify the field type and length, and use the Field Calculator to populate the new field. For more detailed information, please refer to ArcGIS Help: Calculate Field.