Problem with datatype in UI5 Task

Dear Experts,

I am trying to create a UI5 Task for a BPM process. When I try to access the InputData of the task via:

http://bpm:50000/bpmodata/taskdata.svc/taskid/InputData('taskid')?$expand=MyDataType&$format=json

I am getting this error:

[EXCEPTION]

java.lang.IllegalArgumentException: com.sap.bpm.odata.exception.ConversionException: Data types with open content are not supported for Task Data. Illegal data type: DataTypeWrapper

at com.sap.bpm.odata.TaskDataEdmProvider.<init>(TaskDataEdmProvider.java:93)

at com.sap.bpm.odata.BPMODataServiceFactory.createService(BPMODataServiceFactory.java:50)

at com.sap.core.odata.core.rest.ODataSubLocator.handle(ODataSubLocator.java:122)

at com.sap.core.odata.core.rest.ODataSubLocator.handleGet(ODataSubLocator.java:35)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:597)

at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:180)

at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:96)

at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:198)

at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:261)

at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:100)

...

What is an "open content"? I don't understand what is wrong with my data type.

Thanks and Regards,

Koray