Description:
As seen in the attached (Filename: RegisterApplicationError.jpg), Register Application page shows errors when the user is registered, but not part of an Organization.

You can confirm that this is the case by:

1). Log into Joomla Backend Administrator as the Host Admin.
2). Navigate to Users->User Manager
3). Search for the user in question.
4). You will see that this user is registered but not part of any organization. The attached (Filename: userManager.png) file shows the behavior.

1). From the Joomla frontend login as Host admin.
2). Navigate to the Organizations page and search for the Organization that this user should belong to.
3). Open the Organization and navigate to the end of the page where Members are listed. Click on “New member”.
4). The “New Member” page is shown. Input the required values in the page and save.
5). While saving, if the system shows throws the error: "A user profile for this Joomla user is already exists.", then do the following:
     a). Login to Joomla backend Administrator as Host admin.
     b). Navigate to Users->User Manager and search for the user in question.
     c). Edit this user and remove him from the organization.
6). Repeat Step#1 to #4.

How to resolve errors while registering an Application in Joomla Porta.