Unable to Execute DDE command from windows service from windows 7 OS

Question

HI

Could you please help me to get resolve  issue, that i am facing from last 2 days but no result.
objective of my program is to run the DDEexecute command from excel app using ms.interop.excel.dll ,

i am able to run the same execution code from button click on Windows 7 OS machine. but unable to execute the same code from the windows service on windows 7 os.( i build the windows service  on DEbugh any CPU mode)
pls find the code for reference.
/* This method performs DDLExecution using the Excel Interop Library.


public void DDLExecuteMethod(string HPServicemgrstring)
{
var excelApp = new Excel.Application();
int nChannel;
nChannel = excelApp.DDEInitiate("HP_Service_Manager", "Actions");
excelApp.DDEExecute(nChannel, HPServicemgrstring);

// excelApp.DDEExecute(nChannel, "[SystemEvent(""ReceiveInteraction"", ""Caller Name"", ""a469116"" ,""Authentication"", ""1111"" ,""LiveOpsID"", ""123"" ,""CallVariable"", ""1"")]");
excelApp.DDETerminate(nChannel);
excelApp.Quit();
}