I am putting together a fresh development virtual machine image running CRM 2016 for my developer team. I also wanted to install and configure ADXStudio Portals as we are planning more projects using this technology.
I setup Dynamics CRM 2016 and named my default organization “TEST”. Brought up CRM with no issues. I decided to deploy another clean CRM org and called it “PORTAL”, as this was going to be the clean CRM organization with Portals loaded.

When I browsed to the organization, I got a weird error:

So I investigated the error log, and found a weird compilation error:
Exception message: c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config(389): error CS0234: The type or namespace name ‘Linq’ does not exist in the namespace ‘System’ (are you missing an assembly reference?)
That was really weird. Thanks to some Googling (YEAH! I use GOOGLE, not BING, get over it!), I stumbled upon this KB article from Microsoft:
https://support.microsoft.com/en-gb/kb/3084967

So apparently “PORTAL” is an organization name that will cause issues.
So I created a new org called “ADXDEV” and all was well.
I hope this info helps someone out!
Cheers
Nick