If you are certain your application is complete, then please keep trying to submit. It may be that there is a lot of web traffic or that your connection is slow or has timed out. Often however, it is because your application is not absolutely complete. Perhaps you have not electronically "signed" the declaration on the last page or there is some information missing from one of the sections. The icon by the section headings on the left hand side menu of the screen will be displayed in green if that section is complete.