shinkan That is because Construct uses power of 2 for spritesheeting. So, in your case, 3 64x64 images are smaller than one 128x128 image. Also, two 258x17 can`t be on a sheet that is lower size than 512, because 512/2 = 256, your image is 2 pixels too wide. And considering that Construct uses 1 pixel each side for sheeting, the max size for a 512x512 sheet would be 254.
Hope I could help you, and sorry for my "engrish", I am Brazilian.