January 8, 2013: I've heard multiple reports of the Space Center Great Work having difficulty pulling in the 300 workers required for it to function. I don't know if it's an official bug, but if you're having the same problem, you're not alone. It only happens with the Space Center. The other Great Works are working out ok. Leave a comment if you're having the same difficulty.
February 5, 2014: The developers are aware of the issue and there has been some suggestions by users that it is related to specific maps. You can read more about this bug on the SimCity messageboards.
April 22, 2014: Mark Johnson over on the SimCity messageboards has been testing out the Space Port great work and finding out which maps it can be built on, and which it doesn't. He's compiled the following list. (Source) Note: I haven't tried to build this GW since I started hearing reports of the bug. If you have success or failure with any of the regions below, please post a comment so we can get additional confirmation back to Mark Johnson.
September 13, 2014: Mark Norris of the SimNation Guild found a solution on a Japanese website describing a work-around that gets the 300 workers to the construction site. It works! You can read more about it on my Space Center Great Work-around page.
Great Work Syncing Bug:
Several updates ago there were many issues with Great Works not syncing properly. This issue has been resolved, so I deleted that information from this page.