Hi Nageswara;

   A "NULL Object reference" error typically means that a pointer to a variable, object class, etc that was declared  by the PB Developer is not a valid pointer (address). It could also be an internally generated pointer referenced by the PB App that is no longer valid (for an example, a Window name that is referenced but the Window has now been closed, resulting in a Null pointer).

   The fix would be to look at your code in the area of the exception and first of all see what the object pointer is that is causing the exception. Once you have that, look around in your App code where the pointer is allocated. Could there be a condition where the pointer is not set before the failed code executes. On the flip side of the coin, is there somewhere in your App that clears out the pointer (ie: A Destroy command is executed).

    The safe way around the problem is to either wrap the exception code area in a TRY..CATCH or use an IsValid() command on the object pointer before you then try and use it - thus preventing the Null Object condition.

HTH

Regards ... Chris