There are two possibilities.

1) There was an actual collision. This would occur if you download the asset, updated on the client server, and then sent it to the host, but someone else updated the asset between the time you downloaded and when you sent it to the host. In that case get the asset again and make your updates and try again.

2) There is a problem with Web Servers. The default configuration of the web server has post msgs as timing out after two minutes if there is no response, and then immediately it posts the request again. When this occurs on a browser submit of a large asset it can be updated again, while it is still being updated the first time. This causes a permanent collision. You can tell this occurred for an asset if you try to just browse the asset details on the web and you get an error about collision. The workaround to prevent this is to tell the web server to not timeout on a post. Once an asset goes bad like this it requires a DBA to update a field in the database.

If the asset is updated and then you try to perform additonal operations on the asset you should refresh it first, otherwise this exepction can be thrown.

Try

someAsset.Resfresh()

prior to performing additional operations on the asset.