Unable to share my notebook to an user who already has an account.

I have 2 mobile phones and 2 different Zoho notebook accounts ( A & B). When I tried to share one note card I created (A) to my another account (B), I got an error message "Receiver is not a Zoho user". But I have already used such receiver's account (B) to create more than one hundred note cards. Why did I get this error message? I also got problem to share note cards from my account B to A even though I didn't get any error message. I couldn't find any shared note card from my account A.

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Migrate your Notebook data to the new, mobile Notebook.
Zoho Notebook is transforming. The new version will include exciting new features and a completely new user experience. The initial version will be mobile based, available for Android and iOS. A new web version will be available after the initial mobile release. With the release of the new Notebook approaching, we're migrating most of your current data to the new version. Once the new version is released, there will be an additional window to migrate your data. We will not provide access to the