User Session attached to another user's session

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ASP

ASP.NET

C#5.0

I have an asp.net web app and i have an issue when two or more users on the same network are logged in . I use a query to retrieve account details which sometimes retrieves the details of the other person logged in on the same network.

Example

John are Lisa are logged in with different devices and have need used the same device

Sometime Lisa's Account Details appear as John's details on his account and same happens to lisa.

I am not sure if this issue arises from

MembershipUser currentUser = Membership.GetUser();
Guid currentUserId = (Guid)currentUser.ProviderUserKey;

or why lisa can see John's account

Thank you.