Are you using Pre Excel 2003 or 2007+ ?

Also your current formula has errors:

will only sum up column I2:I26 not J too. It should be

If using 2007+ you can change to SUMIFS

Also your current formula has errors:

**=SUMIF('Schedule Variance Data'!$J$2:$J$26,"landlord***",'Schedule Variance Data'!$I$2:$J$26) will only sum up column I2:I26 not J too. It should be

**=SUMIF('Schedule Variance Data'!$J$2:$J$26,"landlord***",'Schedule Variance Data'!$I$2:$I$26) If using 2007+ you can change to SUMIFS

**=SUMIFS('Schedule Variance Data'!$I$2:$I$26, 'Schedule Variance Data'!$J$2:$J$26,"landlord***", 'Schedule Variance Data'!$E$2:$E$26, "OPN")