An internal database error occurred in the Business Data Connectivity Shared service (BDC)

Firstly i want to say that i run across on this error not quite (as i thought) relating to BDC.. but:

My initial goal was simple - create some custom list in SP2010 with Lookup (information already on this site) fields. When i tried to do that i got following message:

So.. BDC service is related with creating Lookup type fields in SharePoint. Time ago we moved our SharePoint databases to new SQL server, but we didn't move our BDC db.. so i started to realize where is the problem. I have to create new BDC service application with new db in our new sql server + delete old BDC application (relationships), point my web application to new BDC service application.

I looked in SP Central Adminstration page for Service Applications (Application management -> Manage Service Applications).

1. Deleted old BDC application.
2. Created new BDC.
3. Point web application to new BDC (Application management -> Service Applications -> Service Application Associations)
4. IISRESET

But unfortuneatlly when i tried to create Lookup field i got new error saying:
Entity (External Content Type) cannot be found with Namespace = '', Name = 'New external content Type'

Solution:

Previously i had some (With old BDC application) External Lists with custom external content types in them, so when we are creating Lookup fields, SharePoitn is looking for those content types and they didn't exist any more, so i DELETED THOSE OLD EXTERNAL LISTS.