The nan error is caused by your save game being corrupted. iGrow game auto saves a lot and if the game is closed while it is saving the game will leave a blank save game file.

If you navigate to your "My Documents" folder on your computer you should be able to see a folder called "iGrowGame". This folder holds all your saved game files. If you locate the folder the same name as the saved games that is corrupted you will find all the data for that save game.

It's possible that your save file that is broken will likely be your "System_Settings.txt" It could be another file but this file keeps track of the in game file which saves the most.

Your "System_Settings.txt" should display something like:

time=2.16;

As this is the recorded days and hours. If the file is blank then this has been corrupted. Depending on the time you have been playing this saved game will determine what you add to the file. If you set the time before your plants were planted then they wont grow and if you change it to after they should have finished they will be complete ready to harvest. So you can harvest your plants and carry on your game as normal. So I suggest making this a lot higher like:

time=999;

Though keep in mind you will need to increase this even more if you file is corrupted again for any reason.

To avoid corruption, always make sure you exit the game through the in game menus.