Error when launching workflow

[Sutty100]

Whenever I try and launch a new workflow via the workflow console I am seeing the following error message coming back as the response and the workflow does not run:

     

Message

java.lang.NoClassDefFoundError: net.fortuna.ical4j.model.TimeZoneRegistryImpl (initialization failure)

I have never seen this error before and we have done the usual restarts etc...has anybody come across this before!?

[smacdonald2008]

Is this Workflow an out of the box workflow or a custom one that uses custom Java libs? 

Can you pls let us know what version of AEM you are using.