For example, something like this fails:
string oldfile = (@"C:\oldfile.txt");
string newfile = (@"C:\newfolder\newfile.txt");
System.IO.File.Move(oldfile, newfile);
Program crashes with "The given path's format is not supported."
EDIT: I'm doing this in a Windows Forms project vs. Console project, does that make a difference? Intuitively I wouldn't think it should, but you never know...
The problem is the mixture of the verbatim string format ( @"..." ) and escaping slashes ( "\" )
The second piece of code
string oldFile = @"C:\\oldfile.txt"
creates a path of 'C:\\oldfile.txt' which is not recognised as a valid path.
Either use the first version you gave
string oldFile = @"C:\oldfile.txt"
or
string oldFile = "C:\\oldfile.txt"