This sounds like the incompatible sync databases bug we fixed in OmniFocus 1.7.3 for Mac, which you can read more about in the 1.7.3 release notes
This fix will be coming to the iPhone in OmniFocus 1.5.3, which we submitted on Friday and which we hope will be posted soon.
In the meantime, you can clean up the corrupt database on your iPhone by removing OmniFocus altogether (unfortunately, 1.5.2 had a bug where Reset Database wouldn't work, also fixed in 1.5.3), then reinstalling it and syncing it with a clean server database. To make sure your server database is clean before you do this, use File->Replace Server Database on your Mac.
Please note that this procedure loses any changes made to the corrupt iPhone database. If you'd prefer to recover those changes instead, please contact our tech support ninjas and we'll help you get them back. They're available by email at email@example.com
, and by telephone at 1-800-315-OMNI or +1 206-523-4152 (10am - 5pm Pacific Time).