KB-1058 SerializationException in application server log

Symptoms

When accessing Tempo, the following pink box error is returned:

A server error was encountered while processing your request. Please try again.

The application server log contains the following errors:

ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/suite]] (ajp-/0.0.0.0:8009-1) 
Exception while dispatching incoming RPC call: com.google.gwt.user.client.rpc.SerializationException: 
Type '[Lcom.appiancorp.suiteapi.type.Datatype;' was not assignable to 'com.google.gwt.user.client.rpc.IsSerializable' and did not have a custom field serializer.
For security purposes, this type will not be serialized.: instance = [Lcom.appiancorp.suiteapi.type.Datatype;@1f5a7cbd
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667) [gwt-servlet-2.7.0.jar:]
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:130) [gwt-servlet-2.7.0.jar:]
    ...
    at org.apache.coyote.ajp.AjpProtocol$AjpConnectionHandler.process(AjpProtocol.java:420) [jbossweb-7.5.7.Final-redhat-1.jar:7.5.7.Final-redhat-1]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.7.Final-redhat-1.jar:7.5.7.Final-redhat-1]
    at java.lang.Thread.run(Unknown Source) [rt.jar:1.8.0_51]

INFO  [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/suite]] (ajp-/0.0.0.0:8009-7) tempoSvcServlet: ERROR: The serialization policy file '/tempo/BB8E60244F72839F9C31728D856B5C74.gwt.rpc' was not found; did you forget to include it in this deployment?
INFO  [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/suite]] (ajp-/0.0.0.0:8009-7) tempoSvcServlet: WARNING: Failed to get the SerializationPolicy 'BB8E60244F72839F9C31728D856B5C74'; a legacy, 1.3.3 compatible, serialization policy will be used.  You may experience SerializationExceptions as a result.

Cause

The web server is not serving the correct static content.

Action

To correct the issue, perform the following:

1. Navigate to <APACHE_HOME>/www/suite/.
2. Navigate to <APPIAN_HOME>/deployment/web.war/.
3. Compare the two directories using a difference checker. Alternatively, ensure that the size of the folder contents from Step 1 and 2 are the same.
4. If they are not the same, copy over the contents from <APPIAN_HOME>/deployment/web.war/ to <APACHE_HOME>/www/suite/.
   Note: The files from these two directories must NOT be merged. Fully replace the pre-existing contents of <APACHE_HOME>/www/suite/ when performing Step 4.

Affected Versions

This article applies to all versions of Appian using a web server.