DTP &1 cannot be executed. See long text.

What causes this issue?

You want to generate a request with data transfer process &v1&. However,
this DTP cannot currently be executed. Possible reasons for this are:
The source or target object have been changed in a way that is
incompatible to the DTP. For example, a field that is in the key of the
error stack or selection list has been deleted from the source.
The source or target object, or the transformation, has been deleted.

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?

Call DTP maintenance and check the DTP. Where necessary, correct the
error and activate the DTP.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.