Why is the CRM Data Storage Limit is at or over 100%?
SalesForce.com (SFDC) has a limit on the amount of data that can be stored for each object.
The Storage Usage for any Org can be reviewed by navigating to: Setup --> Administration Setup --> Data Management --> Storage Usage.
If object percent is greater than or equal to 100%, then there is too much data for that specific object.
If this is a Sandbox org, it is unavailable until the object is brought under 100%. In a production org, 100% is a soft-cap, but it is not recommended to exceed this amount.
Salesforce does not immediately shutdown a Production org, but requests that the amount of data on the object is reduced. Or, additional storage can be added to bring the object under 100%.
To lower the storage percentage of the object, delete or archive older records.
Documentation: Delete, Archive, and Restore Content