Alessandro Crugnola was struggling with an application he was developing (with Flex and PHP) where his local PHP installation worked just fine but his remote system errored on the same code:

Connecting to the service browser I was receiving the error "Channel.Ping.Failed" error and investingating a bit more in the fault message I discovered that the source error was: "The class {Amf3Broker} could not be found under the class path {/var/htdocs/amfphp/services/amfphp/Amf3Broker.php}" and the Amf3Broker php class does not exists anywhere in amfphp!

Despite some default settings he found, though, things still weren't loading correctly. Finally, he found the culprit - mbstring. One server had the setting to overload the strings and the other didn't resulting in the return of corrupted data from the amfphp stream.