Look through your source images for images that are not complete. This is a sign that you are flying too fast for your SD card to write the images successfully. Part of the image matches, enough to get included but then the grey part gets added to the texturing.
This is why reviewing your images before uploading them is important.
The good news is that if you remove a couple offending images it isn't likely going to affect the map too much. In this particular case though about 1 in 8 images has a grey section in it which is not good. It MIGHT work if you take those images out. This is also where having a lot of overlap comes in handy.
Map Pilot provides controls for controlling the speed for which images are taken to accommodate different SD cards.