Problem running Nav 8 (39663) on Win 10

Can anyone help :?: :?: :?:

Recently upgraded to Win 10 from Win 8 and now my RTC install of Nav 8 (39663) will not run.

The service appears to be started, port sharing is on but I keep getting the following:

The Server "DynamicsNav80" was unable to process the request. The application will close

Event viewer doesn't seem to help (or not when I google this problem), but here is the dump from event viewer.....

Server instance: DynamicsNAV80
User: xxxxx\xxxx.xxxx
Type: System.ArgumentException
Message: An item with the same key has already been added.
StackTrace:
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Microsoft.Dynamics.Nav.XmlMetadata.MetadataProvider.LoadLanguages()
at Microsoft.Dynamics.Nav.XmlMetadata.MetadataProvider.GetLanguageIdByAbbreviatedName(String abbreviatedName)
at Microsoft.Dynamics.Nav.Runtime.NCLCaptionStrings.CreateNCLCaptionStrings(String captionML, String defaultValue)
at Microsoft.Dynamics.Nav.Runtime.NCLMetaTable.AssignFromMetaTable(MetaTable metaTable, Boolean databaseConvertedFromNav2013)
at Microsoft.Dynamics.Nav.Runtime.NCLMetaApplicationObject.Populate()
at Microsoft.Dynamics.Nav.Runtime.NCLMetadata.GetMetaApplicationObject(ObjectType objectType, Int32 objectId, Boolean requireCompiled)
at Microsoft.Dynamics.Nav.Runtime.NavSqlMetadata.GetHashesFromTenantQuery()
at System.Lazy`1.CreateValue()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Lazy`1.get_Value()
at Microsoft.Dynamics.Nav.Runtime.NavSqlMetadata.GetTableIdsAndHashFromDatabase(NavDatabase database)
at Microsoft.Dynamics.Nav.Runtime.NavSqlDatabaseSync.GetChangedTableIds()
at Microsoft.Dynamics.Nav.Runtime.NavSqlDatabaseSync.GetPendingTableChanges(Boolean forceUpdate)
at Microsoft.Dynamics.Nav.Runtime.NavSqlDatabaseSync.CheckTableInSync(Int32 tableThatMustBeInSync)
at Microsoft.Dynamics.Nav.Runtime.NavSqlIsamQueryCommand.FindEqual(NavDatabase database, RecordIdProviderRequest request)
at Microsoft.Dynamics.Nav.Runtime.SqlTableDataProvider.TryGetByPrimaryKey(RecordIdProviderRequest request, ReadOnlyRecordBuffer& recordBuffer)
at Microsoft.Dynamics.Nav.Runtime.DataAccess.InternalTryGetByPrimaryKey(RecordIdCacheRequest request, MutableRecordBuffer& recordBuffer)
at Microsoft.Dynamics.Nav.Runtime.RecordImplementation.FindRecordWithoutCheckingValues(DataError errorLevel, NavValue[] primaryKeyValues, FiltersAndMarks filtersAndMarks, Boolean useRecord, Boolean cacheOnly, Boolean calcAutoCalcFields)
at Microsoft.Dynamics.Nav.Runtime.RecordImplementation.GetRecord(DataError errorLevel, NavValue[] values)
at Microsoft.Dynamics.Nav.Runtime.NavRecord.ALGet(DataError errorLevel, NavValue[] values)
at Microsoft.Dynamics.Nav.Runtime.NavSession.GetPersonalization()
at Microsoft.Dynamics.Nav.Runtime.NavSession.Open(Boolean useUserPersonalization, Byte[] licenseToUse)
at Microsoft.Dynamics.Nav.Service.NSService.OpenConnection(ConnectionRequest connectionRequest)
at SyncInvokeOpenConnection(Object , Object[] , Object[] )
at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs)
at Microsoft.Dynamics.Nav.Service.ServiceOperationInvoker.ErrorMappingCombinator(ServiceOperation innerOperation, NSServiceBase serviceInstance, Object[] inputs, Object[]& outputs)
Source: mscorlib
HResult: -2147024809


Only results I managed to find were suggestions on duplicate keys, but I never got this on win8 with the exact same DB, and exact same NAV exe?

Any ideas where to look ?

Many thanks in advance

Dean.