Hello I've had this problem in the past but eventually AMD released a driver update i'm afraid this is a recurring issue with updates and VSR being not supported.
I'm running a 7970 and have always been able to enable it, I actually just had it running until I updated a few hours ago and tried everything including a clean driver install with no luck. I have a 4k TV and always use the VSR mode to run games smoothly at 60hz because as i'm sure you know this card does not support 4k at 60hz.
Right now my desktop display is set at 1080p and it's running below 60hz because I can tell there is considerable lag in my mouse. I am hoping I can get some help with this issue as it's so frustrating I can barely even use my computer because of this now.