Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple Seeds Mac OS X 10.8.4 Beta Build 12E36
Apple seeded the last beta of OS X 10.8.4 last week but Apple just treated developers with build 12E36 not much appears to have changed in this recent release. Currently, Apple are still asking developers to base their focus on WiFi performance, Graphics, and Safari.
If you find anything interesting within the beta let us know, Tips@MacReviews.com