I started receiving this problem this morning. I was talking to someone, just text, when suddenly their online status was no longer shown and it said
"This person has not shared their details with you."
Which they'd have no reason to do that, at all. While I was still trying to figure out what was going on, they even messaged me when they were shown in this state. I thought it was odd, so I just closed and opened up Skype again. I figured that'd solve the problem because some weird stuff has happened before and that fixed it.
A few hours later, it happened again. I closed Skype and restarted it. When I opened it again, my username and password was pre-filled in, but there was an error message above that, saying
Disk I/O error. Right-click the Skype icon in the Windows taskbar at the bottom right of your screen and choose Quit. Then restart Skype. If you keep seeing this error, please contact Skype customer support.
I did as it said, went to the bottom right, hit quit, closing it. When I restarted Skype, the error message was gone and the password field was blank. I put in my password and logged in again, but the problem persists. I've done that several times to no avail, which is what brings me here.
I have no idea what's causing this problem. I've made no system changes today that should be affecting Skype and I've literally had no problems with it before. I keep seeing the error, so here I am.
Try to reset Skype settings.
Quit Skype or use Windows Task Manager to kill any Skype.exe process. Go to Windows Start and in the Search/Run box type %appdata%, press Enter or OK button. The Windows File Explorer will popup. Locate there a folder with the name Skype. Rename this folder to something different, e.g. Skype_old. Restart Skype.
N.B. If needed, you will still be able to re-establish your call history. All data are still saved in the Skype_old folder.