Try this, write your code in between this. This could be permission issue of current user login.
SPSecurity.RunWithElevatedPrivileges(delegate()
{
});
Also, if won't work also write this code
ElevatedsiteColl.WebApplication.FormDigestSettings.Enabled = false;
ElevatedsiteColl.AllowUnsafeUpdates = true;
wb.AllowUnsafeUpdates = true;
and in our finally block we reset the values to its initial state
finally
{
ElevatedsiteColl.WebApplication.FormDigestSettings.Enabled = true;
wb.AllowUnsafeUpdates = false;
ElevatedsiteColl.AllowUnsafeUpdates = false;
}