I need help for random error null object access

I have a problem with an application that works without problems and is constantly used, but once to three times per day have a random error of access to objects that are null.

For example in the following code:

try

    If isnull (object_ole) then

       MessageBox ("Error", "Null Object")

    End if

catch

End Try

The error occurs on the line "If isnull (object_ole) then" in error access to null object. It also gives the same with instance variables, not only with OLE objects. And at other times the error are PBVM126.dll sybase libraries with Windows c000005 message.

Any help will be useful to me

thank you very much