“Grid View Lite is active. We’ve detected that your product image thumbnails are not scaled to size.”
This means that the images shown are downscaled and cropped into a square default size of 148×148 to be shown in grid view, unless you selected a different square size at WPEC’s Presentation admin tab.
You may buy the pro version to get those images automatically downscaled to 148x? or ?x148 without being cropped, as any normally rectangular sized picture would be downscaled.
The other option is to add filters to a plugin to convert the 148×148 downscaled product pictures to 148x? or ?x148, depending if the image largest size is the base or the side, respectively.