Hi,
Can you try to reinstall the website may be this will solve your problem. You can read in this article how to reinstall the website: http://www.lansweeper.com/kb/50/How-to-reinstall-your-Lansweeper-website.html
If you still have problems after this please send the following to support@lansweeper.com:
-program files/Lansweeper/service/errorlog.txt
-program files/Lansweeper/website/app_data/errorlog.txt