Everything looks good so far.
I cannot reproduce this error:
Inner Exception 3
Type: System.Data.SqlClient.SqlException
Message: Conversion failed when converting the nvarchar value 'D0509948C461_A666_' to data type int.
Source: .Net SqlClient Data Provider
… I wonder where the part 'D0509948C461_A666_' is coming from? It must be internal? The error makes sense in that it would not be able to convert that to an Integer (data type int).
There is another identical Topic here, but in that case the value is ‘2C41388957F5_A666_’ … so this must be an internal variable being created on-the-fly.
But I have no issue on my system with creating a Doc Type.
@Tayfun better have the Devs look into this …