I am having the same problem as electro. Here is the contents of the config file.
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<sectionGroup name="userSettings" type="System.Configuration.UserSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
<section name="TDUeditor.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" allowExeDefinition="MachineToLocalUser" requirePermission="false" />
</sectionGroup>
</configSections>
<connectionStrings>
<add name="TDUeditor.Properties.Settings.carDataConnectionString"
connectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|\carData.mdb;Persist Security Info=True"
providerName="System.Data.OleDb" />
</connectionStrings>
<userSettings>
<TDUeditor.Properties.Settings>
<setting name="locality" serializeAs="String">
<value>US</value>
</setting>
<setting name="tdupath" serializeAs="String">
<value />
</setting>
</TDUeditor.Properties.Settings>
</userSettings>
</configuration>
There's no directory listed. My install path is C:\Program Files (x86)\Atari\Test Drive Unlimited
I can get into the program change stuff around and save data but when I go to save car that's when the error comes up. Also if I hit save data then move onto a different car when I come back to the previous one the values have gone back to stock.