Epic's Steven Polge has updated the Unreal Technology page with word on a problem users are experiencing when connecting to a version 401 Unreal Tournament server, a beta version that was never officially released. Here is the description, as well as what to do when you are playing a regular version 400 or 402 server and still get bitten by the same bug:

If your server is running version 401, it is not 100% compatible with 402 clients. 401 was a beta patch that was never publically released. Please upgrade your servers to 402!

We believe this is the cause of 402 clients getting the following crash in network games:

Critical: appError called:
Critical: Assertion failed: ActorClass [File:E:\unreal220\Engine\Src\UnChan.cpp] [Line: 714]
...

If you get this error while playing, check the version number of the server to which you were connected. If its version is 400 or 402, please send a bug report to utbugs402@epicgames.com - include the server version, the map you were playing, and your unrealtournament.log file.