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
Dropbox Turned Down A Offer From Steve Jobs To Become a Part Of Apple –
Forbes has recently backed up a recent rumour in which suggested that Apple had tried to buy the start up Dropbox. It started back in December 2009 in which Steve Jobs invited Houston and his partner, Arash Ferdowsi ( Founders of Dropbox), for a meeting. Both of the founders were already well know in Silicon valley after there start up Dropbox launched. Even though both founders looked up to Steve Jobs they made it clear they wanted it to remain independent company and would not even sell to Apple
Steve Jobs supposedly offered $800 million to Dropbox who has recently been valued at $4 billion.