Could you post the steps (what you did before saving) so that Ash might take a look into it when he gets back ?
Normally, I have my level designed with sprites. Then I saved as project with folder option . After then I had no preview more and an error message. Also after reopening my project an error message and all the sprite without content. actually the same thing for what you here warn. The difference, I use r60 not r59
I have now saved my project as single file and it works for me. <img src="smileys/smiley1.gif" border="0" align="middle" />
I do not want to once again to save the project with folder to recreate the error for an analyse.
I'm in a creative phase and do not want lose my work again.