Please check release statuses

What causes this issue?

The Customizing settings for the release procedure must be made in the
proper manner.
The settings are either incomplete or faulty (e.g. due to subsequent
changes).

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Please therefore also check the release statuses when maintaining the
release strategy.

Error message extract from SAP system. Copyright SAP SE.