I put a one hour Camtasia video up for a customer today and it wasn't loading. It would show all the signs it was working with the controls and what-not showing up, but the flash video itself (the FLV) wasn't loading.

I checked the IIS logs (always check the logs!) and saw a 404 when index.flv was requested. I knew the file was there, but the request ended in a 404. I also checked the UrlScan logs to see if we weren't applying a whitelist. We weren't.

Turned out that there was no mime-type applied for the FLV extension. Added it, and poof, worked. Ah, life's little details.