Depending on the type of the license you have (floating or node-locked), solving the issue could be either as simple (in case of node-locked) as specifying full path to the license file (e.g. C:\Program Files\PTC\Licensing\lm_12345.txt) in the 'License server' field or a bit more complicated (you would have to install license server and specify the address of the license server like '7788@server_name', where 7788 - standard port used by flexnet in the 'License Server' field).
