F-secure key installer gives a error code 2503 and 2502. It doesn't install the software. What to do?
Looks like you should try running it as an administrator.
For example, after downloading F-Secure Key installer (good to save it on filesystem) - rightclick FSecureKeyWin.msi and choose "Run As Administrator".
If it is not helpful - good to check whether your UAC level is enough high or not (good to choose default or higher):
Back with reply if this suggestion is not applied to your experience!
By the way, good to restart system before try to install F-Secure KEY. At least, if your system is Windows 10.