Unable to send test mail. Error when running Send Scheduled Mailings.

[joelcomit]

Suddenly, I'm not able to send test emails. One moment I could, and the next I couldn't. I get an error that says an error occurred and information could not be saved. I'm also getting the following error when I try to run Send Scheduled Mailings:

Fatal error: Call to undefined function mb_strtoupper() in ...public_html/wp-content/plugins/civicrm/civicrm/packages/html2text/rcube_html2text.php on line 703

I was able to run last night. Only thing that has changed is that WordPress auto updated to 4.1.2. I'm running CiviCRM 4.6.2.

[joelcomit]

I had my support guy recompile apache with the mbstring php extension. Seems to be working again.