Here’s the line from App.Config:
<add key="CheckFileFormatString" value="P{0}\t"{1}, {2}"\t{3}\t{4}\t{5}\t{6}\t{7}\t{8}\t{9}\t{10}"/>
Here’s the code that puts it into a string (please ignore the deprecated .AppSettings.Get call, unless that’s the problem):
string format = ConfigurationSettings.AppSettings.Get("CheckFileFormatString");
…and here’s the resulting string:
P{0}\\t\"{1}, {2}\"\\t{3}\\t{4}\\t{5}\\t{6}\\t{7}\\t{8}\\t{9}\\t{10}
Where’s the extra backslash coming from?
\t is the symbol for a tab in C# etc, but this is not the case in XML. Your \t is being interpreted as two characters. Try replacing \t with
	in your config file.