Media not loading after migrating to the 7.1.2

Hi,

I have migrated an Umbraco instance from 6.1.5 to 7.1.2 Everything went well except media section. Media items does not load and it shows following error message.

Much appreciate if anyone could help

message in the umbracoTracelog

2015-02-23 15:25:38,173 [13] INFO  Umbraco.Core.Persistence.UmbracoDatabase - [Thread 21]    at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at Umbraco.Core.Persistence.Database.MultiPocoFactory.CallCallback[TRet](Delegate callback, IDataReader dr, Int32 count)
   at Umbraco.Core.Persistence.Database.<>c__DisplayClass1a`1.<CreateMultiPocoFactory>b__19(IDataReader reader, Delegate arg3)
   at Umbraco.Core.Persistence.Database.<Query>d__1c`1.MoveNext()