First Check You Connection String
Insted of
<data source="TISATASNIM-PC\SQLEXPRESS;Initial" catalog="ImageViewer;Integrated" security="True" />
<data source="TISATASNIM-PC\SQLEXPRESS;Initial Catalog=ImageViewer;Integrated Security=True" />
Write Connection string like this
<add name="con1" connectionstring="Data Source=IICSS20\PMIS;Initial Catalog=PMA170711;Integrated Security=True <br mode=" hold=" /> providerName=" system.data.sqlclient=" /><br mode=" con="].ConnectionString);</xml>"></add>
IN Code Behind:
Load Connection string like this:
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["con"].ConnectionString);