If a big number of employees resigned at the same time, does that mean there is a problem with the management?

Possible.

Does the smoke emanating from a place indicate that everything is NOT fine?

However much the reason may be vague or concrete, there is always a reason for every action taken by individuals or groups of individuals. If it were only an individual who left, question marks would be put on both the individual & management until the matter is throughouly investigated to its root cause BUT if so mamy employees leave at the same time, the question marks are put on management. Therefore in this case, the management might be in the wrong thus an independent credible commision can be put in place to investigate this matter upto its root cause.

Thanx for the invitation

Thanks for the invitation.

Situation explained indicates that there is a problem with the management . Another reason could be the leader of the group of employees resigning is joining another company with his trusted team or he / she is starting his or her own business and taking the team along. 

Sure

Managers should be aware of the positive atmosphere in the work place

Such a scenario would definitely ring alarm bells and yes, it might be an indicator of management issues. Alternatively, all the resigning employees might have been poached by an expanding competitor!

sometimes could be because of company crises financially, so it is out of management hand. but in this case company vision should make employees be more patience

Yes.

The only exception I can think of is when a competitor pays significantly above the market rate to poach a whole team. 

There won't be smoke without fire.........................

Chances are there or may be it is a sign of a new start up company!

Thanks

No doubt there I a problem and should be solved immedaitely , this case called high turn over , and if top management does not solve this problem organization will be collapsed soon