There are various reasons that this can happen, none that have been confirmed by the manufacturer.
If the install light is flashing, it's usually because the paddle has not been installed in the lid or it's been installed incorrectly. ​
How to resolve the issue...
Take the outer bowl and lid out of the Ninja Creami and take the lid off. If the paddle has not been attached to the lid, attach it. If the paddle is attached to the lid, take it out and put it back in. Make sure the paddle is in correctly and then put the lid back on and insert the outer bowl and lid back into the machine.
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If the install light still flashes, it may be a bigger issue with the machine and you will need contact Ninjja directly to resolve the issue.
You need to contact Ninja directly to resolve this issue.
Contact Ninja through their customer service phone number.
Warranty number: 1-866-826-6941
Customer Service US: 1-800-365-0135