Please Help !! IIS Event 1309 always happen on DFS Shared Namespace Site

My server environment setup :

Server 1: DC1 , DNS, DFS Namespace Server & Storage (iSCSI)

Server 2: DC2 , DNS, DFS Namespace Server & Storage (iSCSI)

Server 3: IIS NLB Webfarm

Server 4: IIS NLB Webfarm

Server 5 & 6: SQL Server Failover Cluster

All running Windows Server 2008R2,

IIS hosting ASP.Net 4.0 Application using Shared Configuration and SMB shared path.

Basically everything work fine, but sometime I got HTTP 500 runtime error, I check the event log file and seen:

Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 24/3/2013 17:17:53
Event time (UTC): 24/3/2013 9:17:53
Event ID: 7f2d827e473a43e1bb2ac4a92b459226
Event sequence: 1
Event occurrence: 1
Event detail code: 0
Application information:
    Application domain: /LM/W3SVC/4/ROOT-60-130085902710723704
    Trust level:
    Application Virtual Path: /
    Application Path: \\xxxxx.com\iis\Content\XXXXX\
    Machine name: WEBFARMB
Process information:
    Process ID: 1420
    Process name: w3wp.exe
    Account name: IIS APPPOOL\Hosting_4_I_64
Exception information:
    Exception type: HttpException
    Exception message: Server cannot access application directory '\\xxxxx.com\iis\Content\XXXXX\'. The directory does not exist or is not accessible because of security settings.
   at System.Web.HttpRuntime.EnsureAccessToApplicationDirectory()
   at System.Web.HttpRuntime.HostingInit(HostingEnvironmentFlags hostingFlags, PolicyLevel policyLevel, Exception appDomainCreationException)

 
 
Request information:
    Request URL: http://www.XXXXX.com/index.aspx
    Request path: /index.aspx
    User host address: XXX.XXX.XXX.XXX
    User:
    Is authenticated: False
    Authentication Type:
    Thread account name: XXXXX\XXXXX
 
Thread information:
    Thread ID: 18
    Thread account name: XXXXX\XXXXX
    Is impersonating: False
    Stack trace:    at System.Web.HttpRuntime.EnsureAccessToApplicationDirectory()
   at System.Web.HttpRuntime.HostingInit(HostingEnvironmentFlags hostingFlags, PolicyLevel policyLevel, Exception appDomainCreationException)
 
 
Custom event details:

It will happen 1-2 times a day, and the site will down around 20 minutes, and then back to normal.

If it happen on Server 3, Server 4 is normal, the site still running on Server 4 and vice versa.

But during the error all shared path is accessible without any issue, I can access via explorer but IIS cant....

Totally no ideas, please help and sorry for my bad english....