In an open STEP 7 project, the options (Display, Filter, Generate, Delete) in the menu item "Tools > Reference data >" are disabled and the cross-references cannot be displayed.
The reason for this behavior might be an incorrect setting in the project properties.
To reactivate the options in the item "Reference data" and have the cross-references displayed again, you must set the entry "STEP 7" in the project properties under "Use".
To check the setting and change it if necessary, select your project in the SIMATIC Manager and right-click to open the project properties. In the "Use" field, change the setting from "PCS 7" to "STEP 7".
Fig. 1: Changing the project properties