declare @t table (i int)
print @t
-----------
Msg 137, Level 16, State 1, Line 2
Must declare the scalar variable "@t".

set @sql = 'ParseMessage' + (select replace(MessageType,'.','') from INSERTED)+ ' '+@inserted
EXEC (@sql)

alter trigger dbo.trig_ins_mt
on dbo.MessageReceive
after insert
as
begin
 set nocount on;
 
 declare @inserted as InsertedTableType;
 declare @proc sysname;
 
 insert into @inserted
 select
  *
 from
  inserted;
  
 declare c cursor local fast_forward for
  select
   'ParseMessage' + MessageType
  from
   inserted;
 
 open c;
 fetch next from c into @proc;
 while @@fetch_status = 0
  begin
   exec @proc @inserted;
   
   fetch next from c into @proc;
  end;
 close c;
 deallocate c;
end;