new site wont' let new user sign in and register

Starting over I have removed old folders, created new multisite, added wpmu dev dash board, then went to create new test site, activated 2012 temp. received email with username and password, clicked on login link, entered information and received Internal Server Error 500. I went to new site through admin panel and got image below. Went to error log and have this message: Cannot load Zend Extension Manager – it was built with configuration 1.2.0, whereas running engine is API220090626,NTS

Failed loading /usr/local/zo/4_3/ZendOptimizer.so: /usr/local/zo/4_3/ZendOptimizer.so: undefined symbol: empty_string

What am I doing wrong and what can I do to make it right?