In general, this error will occur when DAB (Application builder) and content server/webtop/da are installed on the same machine.
App Builder and ACS server use common jar file ucf-server-api.jar. In the classpath for ACS Server, the ucf-server-api.jar located in Program Files\Appliaction Builder\lib directory has precedence over the same jar file present in ACS server webapp lib directory.
There are two "ucf-server-api.jar" if App Bulider is also installed on the machine where CS is installed.
1.$DOCUMENTUM\product\5.3\tomcat\webapps\ACS\WEB-INF\lib
2. Program Files\Documentum\Application Builder\lib
To resolve this:
1. Stop the Method Server
2. Rename the ucf-server-api.jar present in the App builder lib directory
3. Start the Method Server.