When running through an exchange server upgrade  . the /preparead step fails with :

The following error was generated when “$error.Clear();
if ($RoleDatacenterFfoEnvironment -eq “True”)
{
Install-CannedRbacRoles -InvocationMode $RoleInstallationMode -DomainController
$RoleDomainController -IsFfo
}
else
{
Install-CannedRbacRoles -InvocationMode $RoleInstallationMode -DomainController $RoleDomainController
}
” was run:
“Microsoft.Exchange.Data.Directory.ADPossibleOperationException: Active Directory operation failed on xxxxxxx. This error could have been caused by user input or by the Active Directory
server being unavailable. Please retry at a later time. Additional information: Additional information: A required audit event could not be generated for the operation.
Active directory
response: 000021B1: SvcErr: DSID-0315154A, problem 5005 (UNABLE_TO_PROCEED), data 0
. —> System.DirectoryServices.Protocols.DirectoryOperationException: An operation error occurred.
at
System.DirectoryServices.Protocols.LdapConnection.ConstructResponse(Int32 messageId, LdapOperation operation, ResultAll resultType, TimeSpan requestTimeOut, Boolean exceptionOnTimeOut)
at
System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request, TimeSpan requestTimeout)
at Microsoft.Exchange.Data.Directory.GuardedDirectoryExecution.Execute[T](String
bucketName, Func`1 action, Int64& concurrency)
at Microsoft.Exchange.Data.Directory.PooledLdapConnection.GuardedSendRequest(String forestName, GuardedDirectoryExecution
guardedDirectoryExecution, DirectoryRequest request, TimeSpan timeout, Func`3 sendRequestDelegate, Int64& concurrency)
at
Microsoft.Exchange.Data.Directory.PooledLdapConnection.SendRequest(DirectoryRequest request, LdapOperation ldapOperation, Nullable`1 clientSideSearchTimeout, IADLogContext logContext, Boolean
shouldLogLastFilter)
at Microsoft.Exchange.Data.Directory.ADDataSession.ExecuteModificationRequest(ADObject entry, DirectoryRequest request, ADObjectId originalId, Boolean
emptyObjectSessionOnException, Boolean isSync)
— End of inner exception stack trace —
at Microsoft.Exchange.Data.Directory.ADDataSession.AnalyzeDirectoryError(PooledLdapConnection
connection, DirectoryRequest request, DirectoryException de, Int32 totalRetries, Int32 retriesOnServer, String callerFilePath, Int32 callerFileLine, String memberName)
at
Microsoft.Exchange.Data.Directory.ADDataSession.ExecuteModificationRequest(ADObject entry, DirectoryRequest request, ADObjectId originalId, Boolean emptyObjectSessionOnException, Boolean isSync)

at Microsoft.Exchange.Data.Directory.ADDataSession.Save(ADObject instanceToSave, IEnumerable`1 properties, Boolean bypassValidation)
at
Microsoft.Exchange.Data.Directory.SystemConfiguration.ADConfigurationSession.Save(ADConfigurationObject instanceToSave, String callerFilePath, Int32 callerFileLine, String memberName)
at
Microsoft.Exchange.Management.Tasks.RoleUpgrader.SaveRoleAndSuggestCleanupOnFailure(ExchangeRole role)
at Microsoft.Exchange.Management.Tasks.RoleUpgrader.UpdateCannedRole(ExchangeRole
existingRole, ExchangeRole cannedRole, RoleDefinition roleDefinition)
at Microsoft.Exchange.Management.Tasks.RoleUpgrader.CreateOrUpdateRole(RoleNameMapping mapping, RoleDefinition definition,
List`1 enabledPermissionFeatures, String suffix, String mailboxPlanIndex)
at Microsoft.Exchange.Management.Tasks.DeprecatedRoleUpgrader.CreateOrUpdateRoles(RoleNameMapping mapping, List`1
roleDefinitions, List`1 enabledPermissionFeatures, String suffix, String mailboxPlanIndex)
at Microsoft.Exchange.Management.Tasks.DeprecatedRoleUpgrader.UpdateRoles(List`1 rolesDefinitions)

at Microsoft.Exchange.Management.Tasks.InstallCannedRbacRoles.UpdateRolesInOrg(RoleNameMappingCollection mapping, RoleDefinition[] roleDefinitions, ServicePlan servicePlan)
at
Microsoft.Exchange.Management.Tasks.InstallCannedRbacRoles.InternalProcessRecord()
at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__91_1()
at
Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)”.

The Exchange Server setup operation didn’t complete. More details can be found in ExchangeSetup.log located in the <SystemDrive>:\ExchangeSetupLogs folder.

On the domain controller in question

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\Parameters

Create a Dword 32 Maximum Audit Queue Size

Setting this to Decimal 200000 and restarting the Active Directory Domain Services Service fixed the issue