Resolve 'Not Assigned' Error in SAP ABAP Program

The error is in field symbol. In future if you encounter such issue you can go through the logs created by ST22. It will help you in detail to understand the issue and its root cause. The reason of your error is that the field symbol is not initialized and you are trying to use it. You should have a habit of checking the content before using.

check <field_Symbol> is ASSIGNED