Resources are used for localziation. There's no such resource in the official nopCommerce package. Seems that you made some changes to your source code. Find this resource in your code and replace it with requried one according to official (non-modified) package.
Ok. I can ask them. I probably have to post question on their forum.
Can you help me with something else that what is the way to sell different varieties of same product. So lets say, if I have a same T-shirt in 3 colors, how can I make user to select from colors?