You're right, doesn't work. I trusted the blog myself, so haven't tried. But I just tried on a test database I have and got a similar error.

Try alternative solution (also referenced in the comments to that blog)

http://nathondalton.wordpress.com/2010/08/12/delete-table-data-reset-identities-in-sql/

or solution #1 from the blog itself.

>>>Yeah, but that complains when I have FK constraints set.
>>
>>Take a look at this blog post
>>
>>Delete all data in all tables in a database when you have foreign keys
>>
>>From comment by Denis Gobo to this blog post:
>>
>>

>>-- disable referential integrity
>>EXEC sp_MSForEachTable 'ALTER TABLE ? NOCHECK CONSTRAINT ALL' 
>>GO 
>>
>>EXEC sp_MSForEachTable 'TRUNCATE TABLE ?' 
>>GO 
>>
>>-- enable referential integrity again 
>>EXEC sp_MSForEachTable 'ALTER TABLE ? CHECK CONSTRAINT ALL' 
>>GO 
>>

>
>Hmmm, I run the following:
>
>

>EXEC sp_MSForEachTable 'ALTER TABLE ? NOCHECK CONSTRAINT ALL'
>GO
>EXEC sp_MSForEachTable 'TRUNCATE TABLE ?' 
>GO
>EXEC sp_MSForEachTable 'ALTER TABLE ? CHECK CONSTRAINT ALL' 
>

>
>and I get
>
>

>Cannot truncate table 'dbo.aspnet_Roles' because it is being referenced by a FOREIGN KEY constraint.
>