Read Violation at address xxxxxxxx in "projectFolder.dll" Alert Box occurs suddenly?

Hai I am doing selenium auto testing.In this I have two forms.When I click on the button in form1 ,It naviagtes to form2.When I click the "ok" button in form2,Form2 should be closed and it again naviagtes to form1 and form1 operations should be continued.But When I click on "ok" button in form2 Read violation address 00000000B in porojectFolder.dll module alertbox occurs.Why I am having this alertbox?How to fix this?Anyone please help me.Thanks in advance.