In the formula below, the reference 'Activity Metrics'!$J$6:$J$143 will shift
one column each month:
SUMIF('Activity Metrics'!$B$6:$B$143,'Team Leader Cross Check'!G$8,'Activity
Metrics'!$J$6:$J$143) Returns 98

I'm trying to automate this with the following formula:
=SUMIF('Activity Metrics'!$B$6:$B$143,'Team Leader Cross
Check'!G$8,INDIRECT(ADDRESS(6,6+MONTH(Index!$C$3), 1,TRUE,"Activity
Metrics")):INDIRECT(ADDRESS(143,6+MONTH(Index!$C$3 )))) Returns #Value!

formula cross-checks:
=MONTH(Index!$C$3) Returns 4
=ADDRESS(6,6+MONTH(Index!$C$3),1,TRUE,"Activity Metrics") Returns 'Activity
Metrics'!$J$6

What have I done wrong? Any help is greatly appreciated.