Corrupt sapgui.ini or conflict with older SAP GUI versions. Fix:
The keyword "SAPScript Legacy Text Editor GUI 7.70 download" typically points to the specific SAP GUI 7.70 installation package that retains or re-enables this legacy component. sapscript legacy text editor gui 7.70 download
Starting with version 7.50, SAP moved toward Microsoft Word as the primary editor for Sapscript and Smartforms. If you see a when trying to edit text, it usually means the legacy component is referenced but not installed on your local machine. Corrupt sapgui