Solman 7.1 SP12 - IT Calendar ERROR

Hi

We have just upgraded from 7.1 SP8 to SP12 and we plan on using the new IT Calendar.

This is working ok EXCEPT when I try and schedule a work mode. For example, when in the calendar you can right click on any date and schedule an IT Event or schedule a work mode.

When I click Schedule IT Event it works perfectly.

When I click Schedule Work Mode it brings up an error:

500 SAP Internal Server Error

ERROR: Access via 'NULL' object reference not possible (termination: RABAX_STATE)

Any ideas on why Work Mode is not working?

Thanks
Shaun