make sure you closed everything around PRO.
Here a little guide(windows):
1. Open your task manager with the key combination: ctrl + alt + del
2. Click on task manager
3. Click on "more details" (if you're running win10),
4. Search for PRO64_93 or PRO32_93 (depending on what you use)
5. Right click PRO64_93 or PRO32_93 and press on end task (note to neva: don't know how it's called in english)
6. If no PRO.exe is running you should restart the client and try to log in again
If this didn't help, you'll have to wait until the server is going to be rebooted/restarted