Problem with trigger program - pointer problem

Hi

If you have any idea please help - I don't know now what I did wrong ...
I have an RPGLE program which is trigger program ... monitor every add, change and delete actions and write it to audit file.
Program worked correct.
But than, I added some modification - after writing to audit file I do some additional very small action, check one external file and write to another one file.

And now when I call the program I get message:

CPF8E17
Pointer not set for location referenced.

then
RNQ0222
Pointer or parameter error (C G D F).

Message . . . . : Pointer or parameter error (C G D F).
Cause . . . . . : RPG procedure P55400TRG in program PRTRG/P55400TRG at
statement 452 had an error due to a pointer not being correctly set. The
cause of the error is most likely one of the following:
-- A basing pointer was not set.
-- A procedure pointer was not set.
-- The pointer was set, but the object it referenced has been destroyed.
-- A parameter was not passed to the program containing the procedure.
-- A parameter was not passed to the procedure by its caller within the
program.
-- A pointer offset was greater than the size of the space the pointer was
pointing to.

then RNX1024
An error in the trigger program was detected after WRITE on file F55400.

I read many web pages about this problem and not exactly sure what cause the problem?

In my additional code I didn't add any call statement, I didn't change any other/original call statements, so it is rather not problem with parameters ...

So what is the problem?

Regards

Tomek