As far as webMethods is concerned, port 80 is not reserved / blocked. Probably the OS is blocking webMethods from opening port 80, maybe because another program already has it in use?
The “permission denied” message leads me to believe you are running on Unix/Linux as a non-root user. Ports 1024 and below can only have listeners established by root.
“netstat -a” will tell you if there is already a listener on a given port. But if that were the case, the error message would have said something like “port in use”.