This problem arises when the userlib isn't correctly added to the classpath. You need to explicitly check that
<myprojectdir>/model/lib/userlib/*
is on the classpath (Note the "*" at the end!). This will add all the jar files. I don't know where you're hosting your project, if it's with us we can help you with this, just send your contact person an email.
This is an issue with some older mendix service consoles and other start scripts, you should either update your scripts to use userlib/* or download the latest mendix service console from our documentation pages.
Do you have replication.jar in your userlib directory? Looks like that is missing.