When I try to import J2.5.4 content using K2, I get the following error:

Fatal error: Class 'JSimpleXML' not found in /home/urotoday/public_html/dev/administrator/components/com_k2/models/items.php on line 737

Any ideas on how to fix this?

Trying to import 50K articles...

I do not know what is happening (and will try to look into it when I get home).

Just to confirm: are you using the latest version of K2?

Yes, downloaded it today from the getk2.org site :)

Tried re-installing, no luck.. So far, K2 @fail

Found a solution on RedComponent website of all places...

Edit /administrator/components/com_k2/models/items.php on line 737

change from: $xml = new JSimpleXML;
to: $xml = JFactory::getXMLParser('Simple');

Make sure your PHP configuration has plenty of memory. I had to raise it to 384mb just to get the import working.

OK, for 50k articles, you will reach a max_execution_time limit. So, you will need access to your PHP.ini file to increase that time.

Looks like the K2 import script cannot handle large sites. The import eventually came back with a 500 error after about 5 minutes of running.