enhancing the standard po screen

Hello Gurus,

        I have enhanced the standard PO screen based on logic and added two buttons .I took the help for this link Dynamically Modifying Purchase order FPM in SRM7 using custom AppCC

1. Now I am clicking on tab buttons which I created its giving an error of MOVE_CAST_ERROR.

2. Also based on the value filled I have to update the it on SAVE button of screen /SAPSRM/WDCC_FPM_OIF_PO_PURCH.Now I am not able to get how to update the data of my tab buttons on this save button.Where to code for this on save button.

Thanks

Gaurav Gautam