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Lightning App Builder Trailhead

In Lightning App Builder module  I hade finished all challenge of this module in my trailhead playground.but when i came in last challenge '"work with custom lightning component" i am not able to install the unmanaged package "Contacts Today" in my is giving following error

"This page has an error. You might just need to refresh it. afterRender threw an error in 'lightning:accordionSection' [Cannot read property 'dispatchEvent' of null] Failing descriptor: {lightning:accordionSection}"
when i close it
it display

"This app can't be installed.
There are problems that prevent this package from being installed.
You cannot install an unlocked package without a namespace into an org with a namespace".
Please help me solve this
Khan AnasKhan Anas (Salesforce Developers) 
Hi Jyotsana,

Greetings to you!

Please follow the below steps to install the package:

Important: Please use a new Trailhead Playground for this challenge.

1. Click on the Install Unmanaged Package URL
2. It will redirect you to your base org and will probably show you an error.
3. Copy your Playground or any different org you want to install the package into URL (Ex.: Leave the rest).
4. While installing the package you will get the following URL -->
5. Replace with the playground URL as follows
6. Press Enter the rest process is similar.

Alternatively, you can follow the below steps:

1. Open an incognito browser window in Chrome.
2. Go to Trailhead and log in.
3. Stop and check and make sure you're in an incognito window. Seriously. This won't work without it. 
4. Navigate to the challenge that requires you to install the package or app. 
5. In the Hands-on Challenge section, click the dropdown to see your list of Developer Edition and Trailhead Playground orgs. Confirm that the org with the checkmark is the org where you want to install the package or app.
6. Click Launch to open that org in a new browser window. 
Note: This new browser window must be open before you go on to the next step. 
7. In the Trailhead browser window, click the package or app install link included in the challenge text. Remember that you need to be in incognito mode. 
8. On the Salesforce login screen, enter the username and password for your Trailhead Playground or Developer Edition org. Note: These login credentials are sometimes different from the username and password you use to log in to Trailhead. If you don’t know the username and password for your Trailhead Playground org, check out this article:
9. Follow the AppExchange instructions to finish installing the package or app.

I hope it helps you!

Kindly let me know if it helps you and close your query by marking it as solved so that it can help others in the future. It will help to keep this community clean.

Thanks and Regards,
Khan Anas
Hi Anas
Thanks for your reply
but i already did all these's not working in newplayground also.
Thanks and Regards
Jyotsana Singh