Error using Microsoft application cache block

[Aamir79]

Hi all,

I'm using Microsoft Applications cache block in my web application. It
worked fine for sometime then suddenly it is raising the following error:

Message: "Can't validate the current data item. Maybe it was altered."
Source: "Microsoft.Appl icationBlocks.C ache"
StackTrace: "at
Microsoft.Appli cationBlocks.Ca che.DataProtect ionManager.Remo veMAC(Byte[]
binaryMacValue) in
C:\Inetpub\wwwr oot\myApp\Appli cationBuildingB locks\Microsoft .ApplicationBlo cks.Cache\DataP rotectionManage r.vb:line 260
at
Microsoft.Appli cationBlocks.Ca che.Storages.Mm fCacheStorage.G etData(String
key) in
C:\Inetpub\wwwr oot\myApp\Appli cationBuildingB locks\Microsoft .ApplicationBlo cks.Cache\Stora geImplementatio ns\MmfCacheStor age.vb:line 447
at Microsoft.Appli cationBlocks.Ca che.CacheManage r.GetData(Strin g key) in
C:\Inetpub\wwwr oot\myApp\Appli cationBuildingB locks\Microsoft .ApplicationBlo cks.Cache\Cache Manager.vb:line 310
at Microsoft.Appli cationBlocks.Ca che.CacheManage r.get_Item(Stri ng key) in
C:\Inetpub\wwwr oot\myApp\Appli cationBuildingB locks\Microsoft .ApplicationBlo cks.Cache\Cache Manager.vb:line 128

For storage location i'm using mmfcacheStorage
The message shows that data item is altered but it is not altered and i'm
using the following code.

Dim cacheCountry As CacheManager = CacheManager.Ge tCacheManager()

If cacheCountry.It em("countryCach e") Is Nothing Then 'Error line'
' Add data into cache'
cacheCountry.Ad d("countryCache ", countries)
else
'Assign cache data to a varible
getCountries = CType(cacheCoun try.Item("count ryCache"), countryClass)
End if

Is there someting wrong with code?

looking forward to your reply

Regards
Aamir