An unhandled error occured

Security exception - value of $_GET['SMPagesId'] = 'voreshunde' is in conflict with value restriction 'Guid'

Stack trace
#0 /customers/b/f/0/beaglador.dk/httpd.www/base/SMEnvironment.class.php(156): SMEnvironment::getValidatedValue('$_GET', Array, 'SMPagesId', 'Guid', Array)
#1 /customers/b/f/0/beaglador.dk/httpd.www/extensions/SMPages/FrmViewer.class.php(318): SMEnvironment::GetQueryValue('SMPagesId', 'Guid')
#2 /customers/b/f/0/beaglador.dk/httpd.www/extensions/SMPages/Main.class.php(29): SMPagesFrmViewer::GetCurrentPage()
#3 /customers/b/f/0/beaglador.dk/httpd.www/base/SMController.class.php(462): SMPages->Init()
#4 /customers/b/f/0/beaglador.dk/httpd.www/base/SMController.class.php(128): SMController->autoExecuteExtensions('Init')
#5 /customers/b/f/0/beaglador.dk/httpd.www/index.php(27): SMController->Execute()
#6 {main}