Hi ,
Note: There are three fields of WBS element on the Order. I am assuming that you are not influencing the WBS tab on additional data but other tabs. I do not the exact reason why Additional data tab is not covered in T code OIAZ.
The alternate is the BADI implementation to modify the screen .
SPRO->Plant Maintenance and Customer Service->System Enhancements and Data Transfer->Business Add-Ins->BAdI: Field content and display modification.
Implement the BADI-> IWO1_SCREEN_MODIFY.
Inside the method CHANGE_SCREEN of implementation class write the code to make CAUFVD-PSPEL(WBS) Input disabled .
The code will be .
check IS_CAUFVD-AUART = 'ORTYPE' . "Check the Order type
IF i_screen_name = 'CAUFVD-PSPEL'. "If the screen name is WBS elemnt
screen-input = 0. " Make input disabled
ENDIF.
Please try and let us know the results.
Anjan