Based on your explanation, I assume port 80 is in use by the default website in IIS, in which case you cannot use it for another website in IIS Express as well. You'll either need to choose a different port for the Lansweeper website or choose a different port for the IIS website in IIS Manager.
Based on your explanation, I assume port 80 is in use by the default website in IIS, in which case you cannot use it for another website in IIS Express as well. You'll either need to choose a different port for the Lansweeper website or choose a different port for the IIS website in IIS Manager.