Which version of Pro E are you trying to run?
WF3 and WF4 cannot run with a WF2 license server.
Failing that, try restarting the license server. We have 11 floating licenses here and occasionally we find that the server fails to release some licenses when Pro E is shut down. When all the licenses are used up, we get the message you're seeing.
Running PTC status shows some designers using 2 or more of the licenses. Restarting the server resets the licenses.
Is it just your machine that wont run or are there others that cannot connect? Is the server local to your machine, i,e, in the same building? If not, try putting the servers IP address in as the server name. We have people in China, India and the US that use our license server and they have to use the server IP address to get access.
Have you checked that the server details match the name in the the license text file from PTC. If they matcch the *.lic file will not work.
This is all assuming that you have a real copy of Pro Engineer. Hacking the license server software is often unsuccessful.
Good Luck!
Adrian