The possible solutions for this problem are two.
An old version of the CRM plugin
If you receive Status can't be blank error, and you don't have a status field when creating a Deal, it means that your plugin needs to be upgraded because you use a very old version of the CRM plugin. This problem appears in old versions of the CRM plugin.
Upgrading a plugin to a newer version works exactly the same as upgrading from a free to a PRO version. Please check our article about upgrading.
Please check if all the files from the plugin's previous version are correctly replaced with the new ones.
Deal statuses
The second reason for appearing the warning message is that you haven't created deal statuses yet. Please check this article for more detail how they could be created and added to deals.