I create a BDC entry for a web service that exposes a catalog of publications. Each publication has a collection of authors. When I display the data in Bussiness Data List the column "Authors" displays "BDC.Authors[]".
Ho do I get Sharepoint 2007 to display the last names, seperated by a ","?
I was getting a similar error message once and found out the reason was something regarding the fact that the data I was returning to the BDC was unserializable. I had to fix my web service to return some serializable data (I think String[] is what I used), and it was fine.
Not exactly the same, but maybe it can get you on the right path.