Error 4015 appears, if the Floating License Server has stopped or the connection between the server and the client is disrupted (LAN or internet). Please note that, each time you reboot the server machine the Floating License Server has to be re-started.
To get the current status of the server (if it is a Windows machine), please follow the steps below:

1. Open a command prompt and cd to the directory where the Floating License Server is installed.
2. Run the command ./lmstat -c bin/license/strand.lic -f marray/ genespring
   Please check (in the Task Manager) if the two processes 'lmgrd.exe' and 'strand.exe' are running on the server machine to confirm that the Floating License Server has been started.
3. Once this is confirmed try to connect to the Floating License Server from the GeneSpring GX client.

The Floating License Server should be accessible through the network on the port used by FlexLM, which is between 27000 and 27010, by default.
If the server is installed on Linux or Mac, please refer to the Floating License Server administration details in the FloatingServer.pdf document in the Floating License Server installation directory.