Session value lost

Hi friend,
i am working in Asp.net 4.0,C#,IIS 7.0 and OS- windows 7 or window server 2008 R2.
My application lost session value frequently,even i am working on the page.

Following error log is generated in windows Log.

 Error Log
1. Event code:1001
    Application is starting .
2. An account was successfully logged on.

 

Subject:

                Security ID:                            SYSTEM

                Account Name:                     CARLTON4$

                Account Domain:                 WORKGROUP

                Logon ID:                               0x3e7

 

Logon Type:                                          5

 

New Logon:

                Security ID:                            SYSTEM

                Account Name:                     SYSTEM

                Account Domain:                 NT AUTHORITY

                Logon ID:                               0x3e7

                Logon GUID:                          {00000000-0000-0000-0000-000000000000}

 

Process Information:

                Process ID:                             0x284

                Process Name:                      C:\Windows\System32\services.exe

 

Network Information:

                Workstation Name:             

                Source Network Address:    -

                Source Port:                           -

 

Detailed Authentication Information:

                Logon Process:                     Advapi

                Authentication Package:     Negotiate

                Transited Services:                -

                Package Name (NTLM only):              -

                Key Length:                           0

 

This event is generated when a logon session is created. It is generated on the computer that was accessed.

 

The subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.

 

The logon type field indicates the kind of logon that occurred. The most common types are 2 (interactive) and 3 (network).

 

The New Logon fields indicate the account for whom the new logon was created, i.e. the account that was logged on.

 

The network fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.

 

The authentication information fields provide detailed information about this specific logon request.

                - Logon GUID is a unique identifier that can be used to correlate this event with a KDC event.

                - Transited services indicate which intermediate services have participated in this logon request.

                - Package name indicates which sub-protocol was used among the NTLM protocols.

                - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.