Uh oh....
This could mean you're going down a slippery road. First and foremost you have to have the pinch rollers under the marked areas otherwise it's not going to work and give you the error you're still receiving. My SP300v Has little metal plates where the wheels can go and still be able to touch the driver.
If you have tried what I stated above and it's still not running you might have to do what I did with my printer and replace the cut carriage cable. The part is pretty cheap but unless you are VERY good at reading directions and have a little know how and ingenuity you will have a hard time replacing it.
Hope this helps.
Good luck.