Design Studio 1.6 with multisource universe, Failed to initialize Query Panel

HI,

I am having Design Studio 1.6 and can not manage to add a multisource universe (UNX) as a data source. When asked to edit the query panel I get an error 'Failed to initialize Query Panel'.

The multisource unx is based on a SQL Database and SharePoint lists which are connected via Web Service.

With single source universes all works fine.

See below the error log.

Thank you in advance!