calling elog possibly causing problem in DirectFunctionCall1

Hi ,
In certain C trigger function following code snippet causes ERROR:
---------------------------------------------------
elog (NOTICE , "before calling DirectFunctionCall1");
  data->time_stamp = 
    DirectFunctionCall1(timestamptz_in, CStringGetDatum("now"));
elog (NOTICE , "after calling DirectFunctionCall1");
----------------------------------------------------

begin work;INSERT INTO  audittest.test_table (name,foo) values ('test','test'); rollback;
BEGIN
NOTICE:  before calling DirectFunctionCall1
ERROR:  timestamp(-1073748880) precision must be between 0 and 6
ROLLBACK

If the elog before DirectFunctionCall1 is removed the code works fine. 

begin work;INSERT INTO  audittest.test_table (name,foo) values ('test','test'); rollback;
BEGIN
NOTICE:  after calling DirectFunctionCall1
INSERT 0 1
ROLLBACK

Can anyone please explain how removing a elog makes a difference? 

Regds
Mallah.