I got an Exception after reading Font.FontStyle property of Style Object.

here are the details of the Exception:
Type : System.Runtime.InteropServices.COMException
Message : Unable to get the FontStyle prop0erty of the Font class
ErrorCode : -2146827284
Trace:
at System.RuntimeType.ForwardCallToInvokeMember(Strin g memberName,
BindingFlags flags, Object target, Int32[] aWrapperTypes,
MessageData& msgData)
at Microsoft.Office.Interop.Excel.Font.get_FontStyle( )

Why I'm getting this exception?

Regards,
Raja