Hello,

I am reading a Delta table and exporting it to an external volume. The Unity Catalog external volume points to an Azure Data Lake Storage container.

When I run the code below, I encounter the error message shown below. (When I export the data to a managed volume, the operation completes successfully.)

Could you please help?

Converting to Pandas...
Creating Excel in memory...
Writing to: /Volumes/dev_catalog/silver_schema/external_volume1/outputfolder/competitor_data.xlsx
❌ Error writing to volume: An error occurred while calling o499.cp.
: com.databricks.sql.managedcatalog.acl.UnauthorizedAccessException: PERMISSION_DENIED: Request for user delegation key is not authorized. Details: None
	at com.databricks.sql.managedcatalog.client.ErrorDetailsHandlerImpl.wrapServiceException(ErrorDetailsHandler.scala:119)
	at com.databricks.sql.managedcatalog.client.ErrorDetailsHandlerImpl.wrapServiceException$(ErrorDetailsHandler.scala:88)

!pip install openpyxl

%restart_python

df = spark.read.table('dev_catalog.silver_schema.silver_table')

# For Excel files:
def save_as_excel_to_external_volume(df, volume_path, filename="data.xlsx", sheet_name="Sheet1"):
    """Save DataFrame as Excel using dbutils.fs"""
    import pandas as pd
    from io import BytesIO
    import base64
    
    volume_path = volume_path.rstrip('/')
    full_path = f"{volume_path}/{filename}"
    
    print("Converting to Pandas...")
    pandas_df = df.toPandas()
    
    print("Creating Excel in memory...")
    excel_buffer = BytesIO()
    pandas_df.to_excel(excel_buffer, index=False, sheet_name=sheet_name, engine='openpyxl')
    excel_bytes = excel_buffer.getvalue()
    
    print(f"Writing to: {full_path}")
    try:
        # For binary files, write to temp then copy
        temp_path = f"/tmp/{filename}"
        with open(temp_path, 'wb') as f:
            f.write(excel_bytes)
        
        # Copy from temp to volume using dbutils
        dbutils.fs.cp(f"file:{temp_path}", full_path)
        
        # Clean up temp
        dbutils.fs.rm(f"file:{temp_path}")
        
        print(f"✓ Successfully saved to {full_path}")
        return full_path
    except Exception as e:
        print(f"❌ Error writing to volume: {e}")
        raise
        

volume_path = "/Volumes/dev_catalog/silver_schema/external_volume1/outputfolder/"

save_as_excel_to_external_volume(df, volume_path, "competitor_data.xlsx", "CompetitorData")

 Thanks