Fatal error: Class 'SimpleXMLElement' not found ...

Have this code running for a long time.  We post open jobs to our website, and this allows viewing of existing jobs.  Code running fine since 2014.  Starting Friday (2/23/18), no longer seeing jobs, but this error:

Fatal error: Class 'SimpleXMLElement' not found in /home/stsbbx0/public_html/includes/quickbase.php on line 143

Text of line 143 is:

$xml_packet = new SimpleXMLElement('<qdbapi></qdbapi>');

It looks by the error that "SimpleXMLElement" is now a problem?  Or, is it qdbapi that is a problem?

This code is running on two distinct websites, and both broke simultaneously!  Conclusion is that the websites have not changed, but something in QuickBase has. 

BTW: The separate QuickBase Job Application app still runs OK!

Any ideas?