I'm not entirely sure how this happened. I do remember that I had Extractors on this planet, previously, then decided to change them to Automated Systems. I wasn't happy with how that turned out, so decided to go back to Extractors again, but I somehow have -2 Metal and the game is telling me that I don't have enough resources.
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This is a little bit later in the same game. I can't build Assemblers on my new planet because "not enough resources".
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I deliberately delayed winning the game to test this out a bit. It seems that I could build on other planets, but I couldn't figure out a pattern.