Capcom has indicated that the problem has been fixed, and those who were affected by the issue should not run into the problem for the time being.
Wbacon, a Steam user and Capcom Community Manager, made a Steam announcement indicating what the issue was here. Basically, the 3rd party service of Games for Windows Live, despite not being used in the game directly anymore, had an element left in the Steam version of the game that allowed previous GFWL users to import their old saved games. That connection seems to be at the core of the problem that led to the error message regarding the keys in question, so Capcom requested Valve to disable the missing key system notification so people can get past the error.
However, this may have had side effects. Users on Steam are indicating that they can't seem to import the GFWL version anymore (as that may be related to the disabled message). Community members have pointed out however that there's a patch developed by the community that gets around the issue and fixes some bugs with the steam version as well as region locks on online multiplayer.
Original Story Below
First identified through a post on /rresidentevil, it looks like those players who have purchased or recently activated a copy of Resident Evil 5 over the last 5 days on Steam are running into major problems since Saturday, February 11th, 2017. While the hit Resident Evil 7 may be on people's radar more, recent bundles including older games in the franchise have a new set of players for those old games. Sadly, the only evil zombies those gamers are running into are in the form of error screens, regardless of where the game was bought from, even if you bought it from Steam itself.
User ErikaeBatayz provides a prime example of what's going on. Despite buying Resident Evil 5 over a year ago, he was unable to play the game when he recently attempted to. Specifically, he would get an error message reading: "#SteamUI_JoinDialog_KeyRequestFailed_Text". This is an error message that has been seen time and time again with games such as Final Fantasy XIV: A Realm Reborn and War Thunder. The problem is associated with the game "running out of keys", even if the player had bought the game over a year ago. The key gets "allocated" the first time the game starts up, so if you haven't played it, it doesn't count against those numbers. It seems that if you played Resident Evil 5 before Saturday, then you were in the clear, even if you uninstalled or reinstalled the game.
Now you may think this is not normal, but this isn't uncommon for older games on Steam that have a surplus of sales at once. This isn't the first time that Capcom has had games have similar problems with key-related issues either, as TechRaptor has reported on games such as Dark Void having similar issues related to key activation problems.
But, what has made the situation worse here is the lack of reasonable response time from Capcom and Valve, as those affected by the change have not heard positive feedback on how to get their issue fixed over the past 5 days. Not only does the Capcom support link that Steam provides lead to a 404 error, but no explanation or comment has been made by Capcom, despite various emails being sent to customer support.
TechRaptor has contacted Capcom and Valve to get their response on their issue and will update the article if we get responses from them or anything changes.