Elixir: (ArgumentError) errors were found at the given arguments

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

# Read the line under the error: it names the argument and the reason
#   * 1st argument: not an already existing atom
#   * 1st argument: the table identifier does not refer to an existing ETS table

# Untrusted strings: map them explicitly instead of creating atoms
case status do
  "active" -> :active
  "paused" -> :paused
  _ -> {:error, :invalid_status}
end

# ETS: the table dies with its owner, so check it still exists
:ets.whereis(:my_cache)

# Inspect the value in IEx before the failing call
IO.inspect(value, label: "arg")

How to diagnose Elixir errors

Elixir errors are shaped by the actor model: a GenServer.call timeout does not mean the server crashed, it means the server was busy for longer than the caller was willing to wait. The right question is usually "what is that process doing?" rather than "why did the call fail?". Because supervisors restart failed processes automatically, transient errors can also hide in the logs while the system appears healthy.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

1. Attach to a running node with iex --remsh and inspect the process: Process.info(pid, :message_queue_len). A growing mailbox means the process is the bottleneck.
2. Use :observer.start() to see the supervision tree, process memory and message queues visually.
3. Move long-running work out of handle_call. Use handle_cast, a Task, or a dedicated pool so the GenServer stays responsive.
4. Check restart intensity. A supervisor that exceeds max_restarts takes down its own supervisor, producing a cascade that looks like an unrelated failure at the top.
5. For compile errors in dependencies, run mix deps.compile --force and check that any required native toolchain (make, gcc, erlang headers) is installed.

Tools worth reaching for

• :observer.start()
• iex --remsh
• Process.info/2
• mix deps.tree
• :recon

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

📖 hexdocs.pm 📖 erlang.org

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