>>> The error is strange, but what is the structure of MyTable_tmp?
>>It's because MyTable_tmp contains two columns of 'text' type?
>
>Yes, I would guess so. May be you need to list all fields you want to insert explicitly.
From BOL:
SQL Server 2005 does not allow for text, ntext, or image column references in the inserted and deleted tables for AFTER triggers. However, these data types are included for backward compatibility purposes only. The preferred storage for large data is to use the varchar(max), nvarchar(max), and varbinary(max) data types. Both AFTER and INSTEAD OF triggers support varchar(max), nvarchar(max), and varbinary(max) data in the inserted and deleted tables.
Against Stupidity the Gods themselves Contend in Vain - Johann Christoph Friedrich von Schiller
The only thing normal about database guys is their tables.