The multipart identifier "tablename.fieldname" could not be bound (#4104)

i have a function in VBA (Access) that passes a sql string into a passthrough query that is server side executed

table name .fieldname = task_backup.activityid

I changed the inner joins and left joins to where statements but this particular sql string crashes with the titiled error folowed by the multi-part identifier "task_backup.activityid" could not be bound (#4104) and then it repeats that one more time in the same message
which i think the second "sub message" is for the null criteria

can soemone please give me a hand and maybe even a quick guide to converting these joins - I though i was going it text book fashion.

INSERT INTO NewTasksBeingAdded ( [Activity ID], [WBS Code], [Activity Name], Area, Line)
SELECT [TASK Excel Data].[Activity ID],[TASK Excel Data].[WBS Code], [TASK Excel Data].[Activity Name], [TASK Excel Data].Area, [TASK Excel Data].Line
FROM [TASK Excel Data]
where [TASK Excel Data].[Activity ID] = TASK_BackUP.[Activity ID] and TASK_BackUP.[Activity ID] Is Null