Error “No clean data columns available for custom fields” or “Unable to Access Page” When Creating Custom Field

When creating a custom field,  “No clean data columns available for custom fields” or “Unable to Access Page” error message can be displayed for the following reasons. 
 
Custom field definition is stored in the predefined area for each object, and when deleted, the space is released. 
 
However, the area is not released immediately. It remains internally as deleted data until hard deleted in the irregular process which is executed when server resource usage is low. 
 
In this status, there is no space in the predefined area. It causes an error when creating custom fields, and field creation fails. 
 

Example:

1. Assume that the maximum number of custom fields able to create per object is 100. 

• 95 custom fields are currently used in this object.
• It is close to the limit. If you delete 10 custom fields and immediately create 15 custom fields, an error message is displayed and creation fails because the area for the deleted custom fields has not been released. 
• A few days later, hard delete was executed. After that, 15 custom fields can be created.

Note: Salesforce currently have no means to confirm hard delete execution.