VAST error code
400 — General linear error
What the spec says
The player could not play the linear creative, for a reason that does not fall into the more specific 40x codes.
What actually causes it
- A media file that is reachable but will not decode.
- A codec the player nominally supports but cannot handle at that profile or level.
- A failure during playback that the player could not classify more precisely.
How to fix it
Download the media file and play it locally. If it plays, the problem is player-side compatibility rather than the asset; if it does not, the asset needs re-encoding.
To see whether a tag would hit this before it runs, paste it into the VAST validator. It reads the XML and reports the conditions that map to this code.
Related codes
Code definitions from the IAB Tech Lab VAST 4.3 specification. Causes and fixes are practitioner guidance, last verified July 2026.