I also periodically got this error. On 2000 SP4.

but the xp_stopmail/xp_startmail worked like a champ!

Thanks

Got some help elsewhere, there was trigger that looked at schemas and had to be removed

IF EXISTS (SELECT * FROM sys.triggers WHERE name = N'Check_Object_Name_Schema' AND parent_class=0)

DROP TRIGGER [Check_Object_Name_Schema]...