con-current access

Hello,

    please give suggestions...   


We are using application server with jsp and servlets in our 
application. We use connection pooling

In code we have the problem like 
we have following tables manager,employee,workAllocated
The manager allocates the work to the employee.The work allocated is 
stored in workAllocated table. The employee replies back as to 
whether he accepts the work or wants a change in work 
allocated to him. The manager can at any time change the work 
allocated to  employees.
Now the problem is this. Manager assigns work to employee1. employee1 
opens the browser and is about to click the button 'accept work' at 
that time the manager assigns the work of employee1 to another 
employee.  The employee1 clicks the 'accept work' button. Here we are 
directly updating the status as 1 in database indicating that 
employee1 has accepted the work whereas the manager has assigned the 
work to another employee. 

What is this problem called is this con-current access problem
We have written code in jsp. So we have to take care of this problem 
by coding how to do that in jsp any idea?
Or is it advisable to use EJB. What are points in favour with regard 
to this problem alone to shift to EJB. How does EJB solve this 
problem better than doing doing ourself by code.

regards
Javid