How to solve “The underlying provider failed on Open” exception

Question:

We have installed a new instance of Identify and we are getting the following exception when we try to add a new connection:

The underlying provider failed on Open.
at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf(Boolean openCondition, DbConnection storeConnectionToOpen, DbConnection originalConnection, String exceptionCode, String attemptedOperation, Boolean& closeStoreConnectionOnFailure) at System.Data.EntityClient.EntityConnection.Open() at System.Data.Objects.ObjectContext.EnsureConnection() at System.Data.Objects.ObjectContext.SaveChanges(SaveOptions options) at System.Data.Entity.Internal.InternalContext.SaveChanges() at Safewhere.IdentityProvider.SqlCache.SqlIdentityProviderCacheManager.YMyAyLcFQ() at Safewhere.IdentityProvider.SqlCache.SqlIdentityProviderCacheManager.InvalidateProtocolConnectionCache() at Safewhere.IdentityProvider.Cache.CachingProtocolConnectionRepository.Insert(ProtocolConnection item) at Safewhere.IdentityProvid...

We have changed the application pool users to local computer accounts instead of network service to be compliant with certain security regulations here. I guess that is the problem.

Any idea what we have done wrong?

Answer:

We believe that lack of permission caused this issue, e.g., http://th2tran.blogspot.com/2009/06/underlying-provider-failed-on-open.html.

Please check if the exception has any inner exceptions that can be found in the Windows event log. Or does Windows also log some other useful events?