that error suggests either dlls are missing from the bin - or that the dll's are blocked. When a file is downloaded from the internet, Windows makes a note of this (i.e. that it comes from a potentially unsafe source). To remove this, you just need to unblock the files by right clicking, going to properties and clicking "unblock" - this is obviously much easier on a single zip file that all the individual files -and then overwrite the existing files.

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I have had problems with r/w access to files and even entire directories not being restored after GoDaddy did an update.  I have had problems where files were not completely extracted.  GoDaddy's FTP file manager is way, way too flaky and does not always overwrite files you think it does.  There is one and only one way I've had success and that is Chris Hammond's App_Offline.htm upgrade method using a solid external ftp client (I use FileZilla).  You MUST have a working install to begin with, though, and a good db.

You can roll back reliably using GoDaddy but only within 14 days.  You will need to roll back in steps; it may be many steps depending on where you started the upgrade from (which you never said).  You need to protect a known-good copy of the db with your life.  It helps if you know what version of DNN it was stable with.  

Remember, GoDaddy goes forward in big steps but rolls back in baby-steps, one version at a time...

Or... you can try to piece it together from where you are, knowing nothing...

Download the upgrade package.  Unblock the zip file.  Extract to your local hard drive.  dll's Cathal says are in the bin directory; you can ftp them from there.