If you use Windows XP or below you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the ASUS Virtual Camera program and then click Remove.
If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the ASUS Virtual Camera application and click on Uninstall.
After that, visit Asus Support page and download and install the latest version of the software. This should fix the issue.