Diagnose Assetto Corsa startup, lobby and join failures

An Assetto Corsa server can be running but absent from the lobby, visible but unreachable, or reachable until the client rejects its content. Treat these as separate stages. This guide applies to the original game; Competizione and EVO instructions are not interchangeable.

1. Identify the first failed stage

Record the server ID, incident time, exact client message and whether any other driver can join.
Read the current startup output from its beginning. Look for the first relevant configuration or content error rather than only the last shutdown message.
Identify whether the process is the stock Kunos server or AssettoServer. Keep implementation-specific errors with the documentation for that program.

If the panel console itself cannot connect, diagnose that separately from a game-client connection. Repeatedly pressing Start can obscure which log belongs to the original failure.

2. When the process exits during startup

Compare the current cfg/server_cfg.ini and cfg/entry_list.ini with your last working copy. Check the track and layout identifiers, permitted car list and available entry slots. Confirm that the requested driver count fits the layout's pits. A newly uploaded archive with an extra enclosing directory can leave files outside the path the server actually loads.

Stop before correcting a configuration, change only the identified error and keep the previous file. Do not remove the whole content directory or regenerate every setting to clear one error. If the template rewrites your correction, ask support to identify its active configuration source.

3. When the lobby or network stage fails

Compare the server's configured UDP, TCP and HTTP listeners with the service's assigned allocations. Listing and gameplay are different checks; success at one does not prove the other is reachable. Give support the exact listener and protocol information rather than asking for every port to be opened.

A listing problem affecting several unrelated servers may be upstream, while a failure confined to your service needs its own logs and settings checked. Avoid changing the public IP, disabling firewalls or installing a tunnelling tool as a first response.

4. When a driver is rejected for content

Kunos documents car and track mismatches after game or server-content updates. Compare the selected car, track layout and exact release on the server and the affected client. Obtain required custom content from its authorised publisher. Test with a known-good content combination during an agreed maintenance window before rebuilding a complex modded race.

For AssettoServer specifically, a missing-car-checksum configuration error is documented by that project's authors. Restore the required legitimate content and follow that implementation's explanation. Do not disable integrity checks just to make the error disappear; its additional settings are not universal stock-server options.

Verify and escalate

After one controlled correction, repeat the same failing action with a normal driver account and retain the resulting log. A successful startup should be followed by an actual track join and short driving test. If the cause remains unclear, send support a redacted error excerpt, implementation name, content versions, affected allocations and UTC time. Keep race settings, results and custom files intact while investigating.