C# Syntax Error

Question

I get a compile error of Newline in constant, but I don't see any issue with the code...can someone please point it out?

if (File.Exists(@"C:\Excel\Excel2010\Reports\" + workbookName[i] + "CompletedFiles\" + userName + ".xls"))

and my code highlights the ".xls" and gives a compile error of Newline in Constant.  What is my issue?