I am trying to set up, and then retrieve a connection string, but i keep getting a blank returned

My App.Config file is:

?xml version="1.0" encoding="utf-8" ?
configuration>
configSections>
sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
section name="Top20.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false"
sectionGroup>
configSections
applicationSettings
Top20.Properties.Settings
setting name="MySalesDatabase" serializeAs="String"
value>Provider=VFPOLEDB.1;Data Source=F:\MYFOLDER\LIVE\DFS.DBC
value>
setting
Top20.Properties.Settings
applicationSettings
configuration
(Ive stripped out all html tags... not sure how to send text with html tags imbedded)

My c# code is:
string x = System.Configuration.ConfigurationManager.AppSettings["MySalesDatabase"];

Tia
Gerard