Possible Scenarios:

1. Attempting to Modify a Running Cycle (Modern Models):
   • In newer Whirlpool models (2019 onwards), the 'Err' code indicates you're trying to change or modify the wash cycle settings while the machine is already running. This is a safety feature to prevent interruptions and potential damage.
2. Door Not Properly Closed (Front-Loaders):
   • For front-load Whirlpool washers, the 'Err' code might signify the door isn't fully closed and latched securely. This is another safety measure to prevent leaks and malfunctions.
3. Other Less Common Issues:
   • In some older models or due to specific internal glitches, the 'Err' code could represent other, less common issues like software errors, motor control problems, or communication failures.

How to Troubleshoot:

1. Identify Your Model:
   • Knowing the exact model name and year of manufacture is crucial. You can find this information on a sticker located inside the washer door or on the back panel.
2. Check the Cycle:
   • If you tried changing the cycle mid-wash, simply let the current cycle finish before modifying settings.
3. Verify the Door:
   • For front-loaders, double-check that the door is firmly closed and latched with a click. Push it firmly until it securely shuts.
4. Reset the Washer:
   • Unplug the washer for a few minutes, then plug it back in and restart the cycle. This can sometimes clear minor glitches.
5. Consult User Manual:
   • Refer to your specific model's user manual for detailed troubleshooting steps related to the 'Err' code. It might offer additional instructions based on your model's functionalities.
6. Seek Professional Help:
   • If the error persists after trying these steps, it's recommended to contact Whirlpool support or a qualified appliance repair technician. They can diagnose the specific issue based on your model and recommend the necessary repairs.

Important Notes:

• Always prioritize safety. If you're unsure about any procedures, especially electrical components, seek professional help.
• The combined presence of other error codes might provide more clues about the issue. Refer to your manual for combined code meanings.
• Depending on your model and age, troubleshooting steps might vary.
• If your washer is under warranty, contact Whirlpool support before any repairs.

I hope this information helps you diagnose and resolve the 'Err' code on your Whirlpool washing machine. Remember, providing your model information would allow for more specific guidance.