Unfortunately, your .sol (save) file got deleted. But there are a couple of things you can do to help insure that this won't happen again...
The first thing: If you launch the Machinarium application and then click anywhere on the screen while pressing the Control key, you'll see a little menu pop up. Click on "Settings." Select the tab along the bottom which shows an icon of a Manila folder with a green arrow. Make sure that the little slider is set to 1 MB or more:
Also, if you're using Safari as your browser, perhaps it's deleting your .sol files. Have you recently cleared Safari's cache? Clearing Safari's cache will delete your progress in Machinarium. Also, check the Privacy tab of Safari Preferences. Is it set to block cookies?
And if you're not really up for restarting the game, you can run Machinarium and, once on the main screen, type 'rebol' (no quotes). This will bring up a row of clickable numbers on the bottom which correspond to the different levels of the game...so you can skip to the level where you'd left off.
