I got this error today.  The fix is simple:

If you have multiple blogs configured, in the post window, you can switch to another blog, and then back to the blog you want and that will cause the Writer to drop the post ID information so you can re-publish as a new post. VIA

Another tip

Currently works with the latest version:

Notes

Replaces the previous FLV Player for BlogEngine.NET. I need some help in defining all of the playable formats.  Right now I have flv, mp3, xml and asp (for playlists). With all of the great embedded players you can now play just about any media file you need to. You can customize how you want the player to display very easily by editing mediaplayer.cs. I coded it for my layout with a smaller width than you may need.

Acknowledgments

A copy with minor adjustments of the great MP3 Player plugin.

Features

Plays flv, mp3 and xml playlist files in an embedded player using JW FLV Media Player.

Notes

• Plays any file type that JW FLV Player supports.
• You can customize every aspect of the player by editing mediaplayer.cs
• By default the player size is 320x240 and it doesn't autoplay

Installation

1. Download the zip.
2. Unzip using any archive manager. At the top of unzipped package you should have two items: "mediaplayer" folder and "mediaplayer.cs" file.
3. Copy mediaplayer.cs into your BlogEngine extensions directory (/App_Code/Extensions).
4. Copy "mediaplayer" folder with all it content into root of your BlogEngine application - this is where you'll upload your media files for embedding also.  Make sure ASP.NET has at least read permissions on this folder. (you can delete the test files after you verify it works - they're not needed)

Using

1. Create a blog post. Add this line anywhere in the post: [ mediaplayer:test.flv ] (without the spaces)
2. You should see something like the embedded player below

Examples

Single FLV

Code: [ mediaplayer:test.flv ]

Single MP3

Code: [ mediaplayer:test.mp3 ]

XML Playlist

Code: [ mediaplayer:http://mirror.video.blip.tv/hot-shows.xml ]

This is a lite CMS.

Official Site Here