SAP Message AD451 - Enter a valid structure name

Diagnosis
Before starting mass activation, it is necessary to announce the ABAP/4
Dictionary objects to be activated to the activator using one of the
allowed input media. The following possibilities exist:
1. Entry of a valid transport request or correction containing theABAP/4 Dictionary objects to be activated.
2. Entry of a table with the structure of table TACOB.
3. Transfer via the memory of filled internal table GENTAB with thestructure of table MAGE.
For more detailed information on the allowed input parameters, refer tothe documentation for report RDDMASG0 and to the ABAP/4 Dictionarymanual.
In this instance, none of the three input media was specified or elsethe incorrect form of the chosen input medium was used.

Procedure
Please check your entry.