'Error Importing' message when opening a specific file

Hi folks, just spent the weekend working on a song and now when I open up the audacity file I get an ‘Error Importing’ message box that says ‘Audacity did not recognise the type of the file’. The data file for the song is there and contains all the files and the actual audacity file itself shows it has the data in it but displays nothing when I open it up and gives this error message. This only happens on this specific file and the other audacity files open fine. Have used Audacity for a couple of years now and never seen this before…very despondant as I have a couple of days work in this file.
Any suggestions or fixes greatly appreciated!

I should say that the error message also says ‘if uncompressed, try importing it using ‘Import Raw’’.