I try to call an ABAP function, but I always get en error message "Incorrect field length for Remote Function Call". My call statement looks as follows:  call "Z_CHANGE_CONFIRMATION_TEXT" In.I_RUECK="1716" In.I_RMZHL="3"  Table.LINES(width:132)="t1"

You probably used "Integer" data type to define the ABAP function module parameters I_RUECK and I_RMZHL. Please use character data type instead. GuiXT always works with character fields.