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Have you gone into Build/Buy Mode to see if it's anything you can grab or delete? Also maybe turn on testing cheats and shift click the circle to see if it can be deleted. In case you don't know, to turn on testing cheats, hold Ctrl+Shift and press the C key. The screen will get slightly darker and you will see what you type in the upper left corner. Type "testingcheatsenabled true" without the quote marks and press Enter. When you're finished, repeat the sequence with "testingcheatsenabled false". Let us know if this helps.