One other thing I forgot to mention is that I looked in the GAC and all of the files that these errors are referring to are not in there.  I looked at another server that has not been upgraded and it has all the assembly files. 

Did the upgrade remove the files from the GAC?

I gather you are referring to the K2 for SharePoint 2010 components.

I have seen quite a few cases over the years of those components not upgrading correctly. I would recommend you try retracting, deleting, re-adding, and redeploying the K2 for SP solutions (http://help.k2.com/displaycontent.aspx?id=4102#).

See if that adds things to the GAC correctly. If not, I'd probably suggest you log a support ticket.

I had a similar issue when upgrading from 4.5 to 4.6.6.

One thing to be aware of is that if there is more than one Web Front End (WFE) on the SharePoint farm you should run the upgrade (K2 Setup Manager) on ALL the WFEs first.

After that is done run the K2 for SharePoint Configuration Wizard in Central Administration.

If you still get the error try the following:

1. Copy the SourceCode.SharePoint.dll to the 14ISAPI hive.
2. Manually browse to the following URL to launch the wizard: http://tCentral_Admin_Site:port]/_admin/k2/ConfigWelcome.aspx

Rerun the K2 for SharePoint Configuration Wizard. On the Post Deployment Configuration step note the instruction to restart the SharePoint Timer Service on all web front ends before updating the features. Continue on to the next step after doing so.

Hello,

Please have a look at the following document it will be able to assist you with work arounds on some of the issues you might be facing.

:http://help.k2.com/kb001588

Kind regards 

Nelly