We encountered this issue while installing vCenter 5.1 The error was as shown: The following port numbers are either invalid or already in use. VMware VirtualCenter HTTP port: 80 Once we stopped the World Wide Web Publishing Service , we were able to continue the install. http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1030445 The information provided in this KB helped to resolve the issue in our case , although we dint have SSRS installed . Only thing i could think of was of the World Wide Web Publishing Service. Hope this Helps.