IMHO, always create properly functioning queries before forms. In this case, it should have revealed the issue before altering form design. The problem could be that
a) including the other table requires you to change the table joins to outer and not inner
b) assuming tables are properly related and normalized, the table needs to be in its own query and therefore perhaps as a subform where it is related to a different query.
c) a Totals or Union query may be the only solution (though I suspect not - just throwing out possibilities).
d) either the first mentioned query or alternate one requires a Unique Values or Unique Records property setting.
e) by "when I put this table in the form" you may be indicating you've created a Cartesian product but you didn't say there was a whole whack of repeating records.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.