.Net oracle connection fail

I have created a web application in .net and the connected database is oracle. it's working properly in the localhost but whin i publish it in to an IIS server, sometimes it's working fine but sometimes it's not. it says that ORA-12545: Connect failed because target host or object does not exist. Tns also perfect.

Server Error in '/' Application.

ORA-12545: Connect failed because target host or object does not exist

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.OracleClient.OracleException: ORA-12545: Connect failed because target host or object does not exist


Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 


[OracleException (0x80131938): ORA-12545: Connect failed because target host or object does not exist
]
   System.Data.OracleClient.OracleException.Check(OciErrorHandle errorHandle, Int32 rc) +340556
   System.Data.OracleClient.OracleInternalConnection.OpenOnLocalTransaction(String userName, String password, String serverName, Boolean integratedSecurity, Boolean unicode, Boolean omitOracleConnectionName) +881
   System.Data.OracleClient.OracleInternalConnection..ctor(OracleConnectionString connectionOptions) +129
   System.Data.OracleClient.OracleConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningObject) +40
   System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options) +31
   System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject) +548
   System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject) +69
   System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) +470
   System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) +108
   System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) +118
   System.Data.OracleClient.OracleConnection.Open() +43
   System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) +121
   System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables, Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior) +160
   System.Data.Common.DbDataAdapter.Fill(DataTable dataTable) +108
   WebApplication1.OracleDatasetTableAdapters.CITY_POSTAL_CODESTableAdapter.GetData() in F:\Achchu\TSR_GEOTrackingSystem\OracleDataset.Designer.cs:9666
   WebApplication1.Site1.SetManu() in F:\Achchu\TSR_GEOTrackingSystem\Site1.Master.cs:140
   WebApplication1.Site1.Page_Load(Object sender, EventArgs e) in F:\Achchu\TSR_GEOTrackingSystem\Site1.Master.cs:38
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +51
   System.Web.UI.Control.OnLoad(EventArgs e) +92
   System.Web.UI.Control.LoadRecursive() +54
   System.Web.UI.Control.LoadRecursive() +145
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +772