Getting Server Error 500 When Trying To Access Network Admin

It just started happening today like magic! I activated the multisite option about 2 days ago. I was able to create one additional site via the Network Admin. Today, I needed to create another one for another user and whenever I tried to access the Network Admin I got a server error 500 and advice to look at my server log. When i did, I found the following:

soulfulwriter.com/wp-admin/network/index.php
PHP Fatal error: Call to undefined function wp_get_current_user() in /hermes/bosweb/web134/b1343/ipg.soulfulwriter/wp-includes/capabilities.php on line 1203 (I checked the PHP.ini file too, just in case)

So, I checked the capabilities.php and it all seemed OK. Then again, my PHP knowledge is very limited. It seems to me that it is telling me that the GET (wp_get_current_user() ) on that line is undefined but the previous code to get to that point does seem to define it.

Can anyone point me in the right direction to fix this? It’s only happening with the Network Admin access. I can access my main site fine. I am use a child theme Atmosphere 2012. OMG, now it is happening on my main site too! I went to check on the name of the theme and when I clicked theme, I got it too! Bloody plug-ins!

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

I have only set up plug-ins that are compatible with my version 3.41 and even before I went multiple, some of them were giving me hell like this one. Another one (Nova QR) put code God knows where because even after deleting it their banner and QR image was appearing in all of my pages. My son who is a developer was able to do some coding trick and finally get it out of this one theme (when I switched to another, it was there again!). Anyway, the original question still valid since this just started happening today and I have not done anything new to the site (not new plug-ins)

I would appreciate your help with the “get” function enigma. Thank you.