HI Shahan,
To give you an idea how this error occurs, you use field F_181 on a certain formula and your formula is on the other Field Area which the printing sequence the formula field area is the first to be printed: For example formula field is on Header Area and Field F_181 is on End of Report.
Formula field and Field F_181 should be on same area or F_181 should be the first to be generated.
Regards,
Lean