Seliev Alright, so before I start, there's something that needs to be explained first. PixelSize errors commonly occur when the person using the mod doesn't have a powerful enough GPU to run the amount of animations or run the size of the sprites in the game. There's a certain limit of size and animation frames assigned, which changes based on how powerful your GPU is.
Now, this isn't a problem I can directly fix for everyone. Simply put, some people can run the number of animations and some people can't. As the majority of people can, I can't really fix it for everyone. There is, however, some way you can fix it, to the expense of missing out on some parts.
Go into Documents > My Games > Cosmoteer > Mods > ultrablast.gcw0.6.1 > Parts and open the file called Parts.txt.
Once you've opened that file, you'll see a list of all of the parts. What you want to do is scroll down to the Weapons section of the file, then comment out (by typing \\ next to the path) the offending parts. Parts that might be doing this include the Beam Cannon, Capital Rocket Launcher, Capital Turrets, etc.