Prompt value (Unknown Error, UnsupportedOperationException)

Hello.

I'm trying to create a Design Studio application where the user selects a value from a dropdown. The selected value is then used in a prompt with the name "EnterDatum" which is used in Three data sources and is set with this code:

APPLICATION.setVariableValue("psEnterDatum", HandelseDatum);

It works fine, the data sources are filtered as expected.

But when I add a fourth data source with the same prompt the application crashes with the errors:
BIBaseRuntimeException: Unkown Error

caused by:

UnsupportedOperationException

What could cause these errors?

I have even changed the fourth data source to be just like one of the other Three that works, i'm selecting the same objects.

Still it's just crashing with the above errors.

I'm going crazy - am I missing something? :-)

I'm using a UNX-universe.

Jonathan