Notice: Array to string conversion in grid.phtml on line 161

I am working on a new module and just received the following notice message when I was trying to open the admin html grid.

The reason of this message is that I just copied the Grid.php from another entity that contains different database columns. So I just removed columns which are not defined in install-0.0.1.php ( especially columns with a custom renderer ) to fix the problem.

Cannot create table column without comments

Today I forgot to set a comment for my new column which broke the complete module setup procedure. Here is one example how you can add a new column to the sales flat table ” sales_flat_order_item “.