Hi Jayneeta,
This sounds to me as if one of your users is in a sales team but the other is not, he is creating the opportunity assigning it to the team of which he is not a member. Therefore when he reopens the database or refreshes his list the opportunity disappears.
The Sales teams are set in a different part of Maximizer to the other groups and permissions. You need to run the distribution list manager to work with the sales team memberships.
Regards,
Nick Welburn
CABC Support