AIF web services and ASP.NET MVC web application

[ist]

Hi,
I have very strange problem with AIF. I have ASP.NET MVC application which consumes AIF WCF web services. My Scenario is: AX 2009 SP1 RU8 running on Windows Server 2012. On that machine I have one AOS which is load balancer. I have another 4 AOS's. Every one of them runs on a different virtual machine, so I have 5 AOS'es over 5 different machines with Windows Server 2012 operation system. ASP.NET MVC application and AIF web services applicatoion pools are running with busines connector account. BC configuration points to the AOS which is load balancer. One of ASP.net MVC application forms (especialy login form) has a problem when the AX client is started. When I stop AX there is no problem. When AX works with one AOS (without load balancer) everithing is OK. The problem is:

Message: <Fault xmlns="http://schemas.microsoft.com/dynamics/2008/01/documents/Fault">
<Code />
<Reason>
<Text xml:lang="EN-US">Request Failed. See the Exception Log for details.</Text>
</Reason>
</Fault>Stack trace: at Microsoft.Dynamics.BusinessConnectorNet.Axapta.CallStaticClassMethod(String className, String methodName, Object[] paramList)
at Microsoft.Dynamics.IntegrationFramework.Service.WcfAxAdapter.SubmitMessageToAx()

I have no idea what's the problem.
Thanks,