problem with triggers

Hy everybody,

I have a problem with 2 triggers.

I work on 3 tables :
table A ==> with one trigger after insert that insert values in table B
Table B ==> with one trigger after insert that insert values in table C
Table C
As I insert values on table A, I have a message that indicates the EXECUTE statement as null.
I wonder if it is because the 2nd insert is sent as the first one is not ended.
In this case, how configure postgresql to accept this second insertion?

Best regards