Hi,
CONSTANTS: c_vertex2(40) TYPE c VALUE '(SAPLZMRM_ITEM_CUSTFIELDS)TAB_TC_DRSEG[]'.
the above statement lets us know if we are in G/L Account tab.
are you trying to update RSEG, RBCO and RBMA at the same time and from any item tab (G/L Account, Material, or Enhanced tab)?
Bet regards,
Pablo