Symptoms

After we upgraded K2 to version 4.6.9 (from 4.6.8) ViewFlow feature functionality stopped working in IE.
We're getting HTTP 404 error in IE 10 browser, "The web page cannot be found" and the URL is the following:

If I paste that link into Chrome I get redirected to the correct URL and I can see the flow of the process correctly.

Error receiving :

WTS0003: The caller is not authorized to access the service.
 

Diagnoses

It looks like when you change the original app pool account used for ViewFlow it doesn't update the config file for the token service and we need to add that account to the Allowed Callers session of the Token Service config file:
 

Resolution

So here is what we need to do to in order to change the ViewFlow to use the Workspace account:

1. Stop K2 BlackPearl server and the K2 Claims To Windows Token Service.
2. Got to the path eInstall Drive]Program Files (x86)K2 blackpearlToken ServiceBin
3. Edit the file K2TokenService.exe.config and locate the section:
<allowedCallers>
<clear />
<add value="DENALLIXK2 Service Account" />

</allowedCallers>

4. It should have the K2 Service account.
5. Change to use the Workspace Service Account or you can leave the K2 Service Account and add the Workspace Service Account. It should be ok with only one account.
eg.

<allowedCallers>
<clear />
<add value="DENALLIXK2 Service Account" />
<add value="DENALLIXK2 Workspace Account" />
</allowedCallers>

6. Save the file.
7. Start the K2 Claims to Windows Service and the K2 Service and test.