How can read encrypted connection string in roleManager ASP.NET

pls help, i don't know how to use a Encrypted ConnectionString with RoleManager in ASP.NET This is code in Web.config.

<connectionStrings>
    <add name="strConnectionString" connectionString="eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k="/>    
</connectionStrings>

<roleManager enabled="true" defaultProvider="CustomizedRoleProvider">
  <providers>
    <add connectionStringName="strConnectionString" name="CustomizedRoleProvider" type="System.Web.Security.SqlRoleProvider" />
  </providers>
</roleManager>   
<membership defaultProvider="CustomizedMembershipProvider">
  <providers>
    <add connectionStringName="strConnectionString" name="CustomizedMembershipProvider" type="System.Web.Security.SqlMembershipProvider"/>
  </providers>
</membership>

And in project I create a library to read web config

private const string ConnectionStringKey = "strConnectionString";
private readonly string SQLConnectionString =
   Security.DecryptString(ConfigurationManager.ConnectionStrings[ConnectionStringKey].ConnectionString);

if I change my ConnectionString like this, it's working:

<add name="strConnectionString" connectionString="server=My-PC\\MSSQL2008; database=MyDB; uid=sa; pwd=passw0rd;"/>

But I want my ConnectionString Encrypted so i use

<add name="strConnectionString" connectionString="eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k="/>

So when i running website it throw error:

System.ArgumentException:Keyword not supported: 'eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k='.
Line 46:   string[] roleNames;
Line 47:   roleNames = Roles.GetAllRoles();

Any one help me find it out or any suggestion ?