Getting SIGSEGV error on opening second window

[Adri]

Who can explain (and fix) me why I get a SIGSEGV error upon opening second window?   
The source code is attached (but is far from finished) and the error appears upon selecting te main menu up and next first option: 'Preferences'. The error reads "In file usb2main.pas at line 139: FormSB2Preferences.ShowModal;".
I have used similair construction before and do not underrstand why the error happens now.   

[egsuh]

Or create second form your self,

SecondForm := TSecondForm.Create(nil);
SeondForm.ShowModal;

[Adri]

Thanks both who replied, and so swift. It works now!