An unhandled error occured

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

Stack trace
#0 /home/ppaul/public_html/base/SMEnvironment.class.php(99): SMEnvironment::getValidatedValue('$_GET', Array, 'SMPagesId', 'Guid', Array)
#1 /home/ppaul/public_html/extensions/SMPages/FrmViewer.class.php(274): SMEnvironment::GetQueryValue('SMPagesId', 'Guid')
#2 /home/ppaul/public_html/extensions/SMPages/Main.class.php(29): SMPagesFrmViewer::GetCurrentPage()
#3 /home/ppaul/public_html/base/SMController.class.php(362): SMPages->Init()
#4 /home/ppaul/public_html/base/SMController.class.php(118): SMController->autoExecuteExtensions('Init')
#5 /home/ppaul/public_html/index.php(22): SMController->Execute()
#6 {main}