Don't panic, just build two queries.
Pretend you're trying to query several tables for data. You've added the correct tables to your query, you can see they're all joined, but instead of data, you see an error message. Your query can't run because of something called an ambiguous outer join.
You're seeing that message because of the join structure in your query. Whenever an outer join points to a table, and that table also participates in another join, your query will fail because Access can't match the records returned by each join.
To solve that problem, you create two queries. The first one takes data from the tables in one of the joins. The second query uses the first query as a record source, plus the table involved in the other join. Let's start by looking deeper into what makes joins ambiguous.