Hi,
Apologies for the inconvenience. I'm guessing you're using JavaScript? If you are, you will need to find tk2dSprite.cs in your project (should be in Plugins/tk2d/sprites), and then manually move tk2dCamera and tk2dCameraAnchor (and nothing else) into this folder (Plugins/tk2d/Camera). The directory doesn't matter, it should just be in the same "place" as the sprite scripts and everything else.
You will probably need to create it if it doesn't exist. Once that happens, everything should go back to normal.
What is happening is Unity stops compiling the rest of the scripts as soon as it encounters that error, and the custom inspectors stop working.
If you run into any problems, or if this doesn't fix it, let me know. If you need quicker support, feel free to use the email (I get push email from there). support at unikronsoftware dot com.