Return A File With Bad Headers?

I've build a MP4Handler. The Mp4 hander selects a correct file from a url.The system works if you work with 'normal' mp4 files.But the problem is the MP4 files are genrated by another program, so i think there's the problem.Right now i returned a test file, then it woks great!Do i return the other file, i get a 412 error if i use it in IE (he shows a 400 error because i deleted the 412 error in the IIS i thought maybe that solves the problem). In IE it doesn't work, but in firefox it works great!In my Fiddler result, the first movie (guid url) is from firefox, and works great. The second with the text/html result (selected row) is from IIS.How can i solve this problem?Or is this the problem?:This entity tag is not recognized by IIS. It only affects version 7.0 of the IIS software.From: http://www.pc-library.com/errors/error-code/412-0x19C/ As coding i use this as base: http://dotnetslackers.com/articles/aspnet/Range-Specific-Requests-in-ASP-NET.aspx I changed The GetRequestedFileInfo with:

public override FileInfo GetRequestedFileInfo(HttpContext context)
{
return new FileInfo(context.Request.PhysicalPath);
}