Session coockies and asp.net
===

In my asp.net aplication i used such settings in web.config

    <sessionState mode="InProc" 
                  stateConnectionString="tcpip=127.0.0.1:42424" 
                  stateNetworkTimeout="10" 
                  sqlConnectionString="data source=127.0.0.1;Integrated Security=SSPI" 
                  sqlCommandTimeout="30" customProvider="" cookieless="UseCookies" 
                  cookieName="ASP.NET_SessionId" 
                  timeout="120" 
                  allowCustomSqlDatabase="false" 
                  regenerateExpiredSessionId="true" 
                  partitionResolverType="" 
                  useHostingIdentity="true">
      <providers>
        <clear/>
      </providers>
    </sessionState>

and 

    <authentication mode="Forms">
      <forms loginUrl="~/login.aspx" 
             defaultUrl="Default.aspx" 
             cookieless="UseCookies"/>
    </authentication>

but sometimes session behaviour stand strange

Users get `http://my.appl.com/S(DGsdgfg453dsgfsdgsdgsd)/mypage.html`
where `S(DGsdgfg453dsgfsdgsdgsd)` key for session for one user, but get him all users. As if `UseCookies = false.`

I restart applicaition and some time it work good. Then again.

What problem with my application?