Okay, this is a bug in starmade but there is a fix.
Go into the starmade folder and then to the blueprints folder. Find the folder with the name of your blueprint and copy that name. Then go inside that folder and then into data. There should be 1 or more files with heaps of jumbled letters in their name. At the end of that jumbled letters should be three numbers, which is usually .0.0.0 what you need to do is delete everything before those three numbers and paste the name of the folder into that spot instead. Hope this helps, but if you need a better explanation then I can just make a video and upload it.
Sincerely,
Gynganynga