Unfortunately there have been a few issues recently where some players have abused fake attacks in order to lock a WW-holder out of their account, such that they cannot respond at all to the real attack. As a quick fix to solve this the developers have taken the move to cancel all fake attacks against a Wonder of the World. Do not be confused if you send a small attack to a WW and it returns by itself without generating a report.
We thank you for your patience and hope that a more permanent solution can be found before too long.
All the best,
US Travian Team