VAST Error 901: General VPAID error
A VPAID (executable) ad unit failed — the legacy interactive ad format that runs code inside the player broke somewhere.
VPAID units are programs, not videos: JavaScript (or historically Flash) the player must execute, which then renders the ad itself. Error 901 covers the whole failure surface — the script didn't load, threw on init, never called back, or died mid-playback.
VPAID is deprecated in favor of SIMID and OMID precisely because this failure surface is huge and opaque. Persistent 901 volume is usually an argument for migrating off VPAID, not for debugging it harder.
Why error 901 happens
VPAID script fails to load or initialize
Blocked by CSP or ad blockers, slow CDN, or the unit throws during handshake before the ad can start.
Environment doesn't really support VPAID
The placement claimed support but the runtime lacks capabilities the unit needs; CTV rarely supports VPAID at all.
The unit's internal decisioning abandons the impression
Many VPAID units run measurement first and quit if criteria aren't met — a conditional-ad behavior reported as 901.
Timeout during the VPAID lifecycle
Players cap each VPAID handshake step; a slow unit that misses AdLoaded or AdStarted deadlines is killed.
How to fix VAST error 901
- 1
Test the unit in a VPAID-capable reference player
Load the tag in a debug player that logs the VPAID handshake. The last event before silence identifies the failing lifecycle step.
- 2
Always pair VPAID with a plain video fallback
Include standard MP4 MediaFiles alongside the VPAID unit so unsupported environments still play the ad.
- 3
Migrate to SIMID/OMID
Interactivity belongs in SIMID; measurement belongs in OMID verification. Both eliminate the arbitrary-code failure surface that produces 901s.
Seeing error 901 on a live tag?
Paste the tag URL or XML — the validator resolves the full wrapper chain, validates the schema, downloads every media file, and shows exactly which stage fails.
Validate your VAST tagVAST error 901 — frequently asked questions
Is VPAID dead?+
Deprecated but not gone. The IAB replaced it with SIMID (interactivity) and OMID (measurement) in VAST 4.1+, yet legacy VPAID demand still circulates — reporting 901s wherever it lands on unsupporting inventory.
Why do VPAID ads fail so much more than regular video?+
A regular video ad is a file; a VPAID ad is a program with a multi-step handshake, third-party script dependencies, and its own internal logic — every step is a failure opportunity that plain media doesn't have.