While designing your product, you may have encountered this onscreen warning after uploading a particular file. At its core, it's letting you know there is an issue with the make-up or composition of the file you're using.
When working with true vector graphic images, the "guts" of the file is a series of complicated curves and elements described purely in math. These curves and their associated colors and shapes are easily deconstructed during the preparation process for screen printing, and therefore are preferred for t-shirt designing on KarmaLaunch.
The file you've chosen to use is a little bit like a wolf in sheep's clothing. On the outside, it appears as if it could be a traditional vector file - however, buried inside is a dot-friendly file, your pal the raster. These raster images can be intensely difficult to process "as-is" when preparing them for printing. Some very common raster file types are jpg, png, gif and bmp. In all but a few cases where these files have been purposefully kept simple, they are not ideal for use on the site.
There are several helpful how-to links through help and in our Forum to guide you through becoming more familiar with vector files and how they're constructed. There are even freebie applications to get you started, like Inkscape.