Symptoms

Intermittently we are facing error when loading a K2 Reporting Webpart: An error has occurred trying to load the settings for the report. N/A:Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=9.0.0.0. Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
 

Diagnoses

There were 4 Sharepoint servers serving as WFEs and traffic was load balanced. The intermittent-ness was due to the 'Microsoft Report Viewer 2008 SP1 Redistributable' package not installed on some of the Sharepoint WFE servers:

https://www.microsoft.com/en-us/download/details.aspx?id=3841

Please ensure that this is installed on all Sharepoint WFE servers as per the pre-requisite: https://help.k2.com/onlinehelp/K2blackpearl/ICG/4.6.11/webframe.html#Prereqs_SharePointServer.html

A possible way to narrow down which WFE server(s) it is, is to add a 'hosts' file entry on your client machine to point directly to each of the WFEs server. For example:

192.168.0.1 portal

Alternate between the IP address to the WFE servers (hence removing the load balancer), close and re-open the browser and site, to see which server is possibly throwing this error. The 'Programs and Features' setting on each servers can also be consulted for this information.
 

Resolution

It was determined that the 'Microsoft Report Viewer 2008 SP1 Redistributable' was not installed on 2 of the WFEs. Installing this on the WFEs missing this package resolved the intermittent behavior.