Free busy issue outlook 2010

I am sorry if i am posting this in the wrong place.

We have exchange 2010 sp3 in 3 sites ( US , UK and Africa)

Users in UK start complaining they are not able to See free busy of US users but can see free busy of UK and African users.

We later identified this could be due to the more no of groups which result in increased token size, so we removed 1 users couple of group membership and  he was able to see free busy of other users in US.

Then we have done a registry change in all CAS server to set MAX token zize 

1. Create the following registry keys on all CAS servers ( Exchange Server 2010 SP1 CAS servers) in the Active Directory site:
   • Path: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
     Name: MaxFieldLength 
     Type: DWORD 
     Value data: 65534
   • Path: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
     Name: MaxRequestBytes 
     Type: DWORD 
     Value date: 16777216

But now users start complaining that they now cant see free busy of africa and US users, This affected only 5 users and all user outlook 2010.

P.S: No luck with OWA also for these users. 

Please suggest.