duplicate id error

The following occured:

I deleted all the products and categories after a fresh install. I tried to add a new product and pressed save, a white screen with an error came up.

It had something todo with a duplicate entry in the database, error number 1036. After this I checked the product section under admin and I saw that somehow Product 1 was back in my product list.

It has something to do with the system having no categories, so I added an category, added a new product, selected the category and everything went smoothly.