Troubleshooting

Error guides

Deep pages for the errors people actually search. Each one covers what you’re seeing, why it happens, and the fix on Windows Server.

• IIS · HttpPlatformHandler HTTP 500 with empty logs AppData Python and app-pool identity kill the process before stdout appears. Use Waitress service mode instead.
• Dash · assets DashRenderer is not defined Component suites 404 under a path prefix. Asset URLs and entrypoints must live under /apps/<slug>/.
• Dash · reverse proxy Dash stuck on “Loading…” Shell loads, app never hydrates. Check server = app.server, entrypoint, and public path prefix.
• Dash · import NameError: dash is not defined You imported Dash but called dash.Dash(...). Use Dash(...) or add import dash.
• Dash · Flask entrypoint cannot import name 'app' Connect wants a WSGI object. Prefer app:server / run:server, not app:app, unless app is WSGI.
• pip · wheels pandas / vswhere / Visual Studio No wheel for your Python — pip tried to compile. Prefer 3.11–3.12 or bump pins; skip Build Tools for pandas.
• Redeploy · file lock WinError 32 on runtime.log The app process still held the log open. Stop iVistaarApp-<slug> and redeploy (fixed in 0.6.9+).
• Streamlit · WebSockets Loads but never interactive UI paints, widgets freeze. Needs WebSocket splice — service mode gateway on 0.6.14+.

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