Hello Priyank,
You can use an another way out to display the dynamic sender text in the smartform. Please follow the below steps:
1. You can create a variable with maximum character limit in the Global Definition.
2. Create a program line and write code to populate that variable with the sender text. (make sure you pass the sender text as import parameters).
3. Create a Text Element, resize and reposition it to the appropriate area on the window, and add that variable as &variable&
Hope this helps...
regards,
Vivek