Unity error - Invalid data file
A web browser may display this error if the Unity data file fails to download. Either the file is being blocked or was corrupted during download.
This error may be returned when the school network system has restrictions on MIME extensions which can be used. The proper way to fix it would be to add unity3d as an allowed MIME type and file extension in the firewall or proxy server.
The MIME type for Unity webplayer content is:
And the file extension for unity webplayer files is: