must declare the scalar variable (sql server 2005).what is this error?

Question

SELECT * FROM [tbl_students] WHERE course_id=@courseId 
                        AND   branch_id IN(646768) 
                        AND  (@firstYrPercent is null OR first_year_percent>=@firstYrPercent)
                        AND  (@secondYrpercent is null OR second_year_percent>=@secondYrPercent)
                        AND  (@thirdYrPercent is null OR third_year_percent>=@thirdYrPercent)
                        AND  (@finalYearpercent is null OR final_year_percent>=@finalYearpercent)
                        AND  (@currentDegeePercentage is null OR current_degree_percent>=@currentDegeePercentage)
                        AND  (@passoutYear is null OR passing_year>=@passoutYear) 
                        AND  (@currentBacklog is null OR current_backlog<=@currentBacklog)
                        AND   gender=@sex 
                        AND  (@eGap is null OR gapin_education<=@eGap)
                        AND  (@highSchoolPercentge is null OR highschool_percentage>=@highSchoolPercentge)
                        AND  (@higherSchoolPercentage is null OR ssc_percentage>=@higherSchoolPercentage)
                        AND  (@grauationPercentage is null OR graduation_percentage>=@grauationPercentage)
                        AND  (@diplomaPercentage is null OR diploma_percentage>=@diplomaPercentage)
                        AND  (@noOfAtkt is null OR number_of_ATKT<=@noOfAtkt)
                        AND  (@date is null OR DOB>=@date)

giving error what is this---- Must declare the scalar variable "@courseId".