CS6 for iMAC keep asking for serial number nearly everyday

There is an iMAC (OSX 10.10) in my company which was purchased 2 years ago with CS6 Design Standard installed.
There was no problem at all after the purchase.
However recently, CS6 keep asking the user to type the serial number nearly everyday(see attached image); the software can be used normally once the serial number is entered.
The user is a general user without admin privilege. Anyway I have tried to closed all adobe products, login with admin account and enter the correct serial number, it works as usual; however after one or two days CS6 still asking for serial again... so I guess this problem shall not related to user account privilege.
I believe my serial key is a volume license key.
Any suggestion? Thanks.


Fix the permissions on the relevant Library folders.
Sign in, activation, or connection errors | CS5.5 and later