Correct an issue with a where clause with calculation

The last or statement in the where doesn;t work.

SELECT DISTINCT Building,
          BuildingName,
          StudentId,
          SECTION_KEY,
            PEIMS_Sequence,
            StudentName,
            CASE PEIMS_Sequence
            WHEN '0' THEN COURSE
            ELSE LEFT(COURSE,DATALENGTH(COURSE)-1)
            END
            AS NEWCRSENAME,
             COURSE,
            CourseName,
            CREDIT,
            SchoolYear,
            StudentGrade,
            SEM1Grade,
            SEM2Grade,
            MailingAddress,
            MailingCity,
            MailingState,
            MailingZip
            from #tmpRC
       where ((PEIMS_Sequence = '0') and ((ISNUMERIC(SEM1Grade) = 1  and  CONVERT(int, SEM1Grade) <= 69) or (ISNUMERIC(SEM1Grade) <> 1  and  CONVERT(varchar, SEM1Grade) = SEM1Grade)) or ((ISNUMERIC(SEM1Grade) = 1  and  CONVERT(int, SEM1Grade) <= 69) or (ISNUMERIC(SEM2Grade) <> 1  and  CONVERT(varchar, SEM2Grade) = SEM2Grade))) OR
              ((PEIMS_Sequence = '1' or PEIMS_Sequence = '2') and ((SEM1Grade IS NULL) and (ISNUMERIC(SEM1Grade) = 1  and  CONVERT(int, SEM1Grade) <= 69) or (ISNUMERIC(SEM1Grade) <> 1  and  CONVERT(varchar, SEM1Grade) = SEM1Grade)) or ((SEM1Grade IS NULL) and (ISNUMERIC(SEM2Grade) = 1  and  CONVERT(int, SEM2Grade) <= 69) or (ISNUMERIC(SEM2Grade) <> 1  and  CONVERT(varchar, SEM2Grade) = SEM2Grade))) OR
              ((PEIMS_Sequence = '1' or PEIMS_Sequence = '2') and ((ISNUMERIC(SEM1Grade) = 1) and (CAST(SEM1Grade AS INT) <= 70)) and ((ISNUMERIC([SEM2Grade]) = 1) and (CAST(SEM2Grade AS INT) > 0)) and (SEM1Grade + SEM2Grade / 2 <= 69.5)) AND
                  (StudentGrade = @Grade OR LEN(ISNULL(@Grade,'')) = 0)