Upon upgrading a SQL Server 2000 to SQL Server 2005 Standard Edition instance –  this error message appeared on a SQL Server trace error event:

Msg 2801, Level 16, State 1, Procedure myTrigger, Line 13

The definition of object ‘myTrigger’  has changed since it was compiled.

The statement has been terminated.

Using a trace I isolated the trigger which caused this error. The developers had created the trigger in the following format:

Alter table appEvent DISABLE Trigger ALL

 <some dml statements >

 Alter table appEvent ENABLE Trigger ALL

When commenting out the DISABLE TRIGGER ALL  and ENABLE TRIGGER ALL  the code works without error – but does have a  data knock-on effect. The developers  explained they wrote this code to avoid creating duplicates in the target data set – fronm other triggers executing.

 The error is occuring because : the ALL option is used which affects all triggers on the table , and as an INSERT statement is used which fires the trigger which actually is doing the ENABLE\DISABLE. This creates the error message as trigger recompilation needs to occur .

 I advised them to use either application logic to prepare data adequately or add other constraints at the table level. 

Source:Jack Vamvas (http://www.sqlserver-dba.com)