The error is self explanatory. You cannot have one section defined twice in a web.config file.
Remove the line:
<add key="ConnectionString" value="Data Source=10.10.10.144;Initial Catalog=clientbackup;User ID=sa;Password='supp0rt';Pooling=False"/>
from
<appSettings> </appSettings>
section. It should work. :thumbsup:
*edit - added explanation.