All I got when viewing certain pages within the Commerce Manager (like the properties of a specific payment method) was Could not load file or assembly 'Microsoft.ReportViewer.ProcessingObjectModel, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

Solution: Pretty simple - install the Microsoft Report Viewer 2010 Redistributable Package from Microsoft.

It might also work with the Report Viewer 2012 runtime, but I have not tried this as it also required some SQL Server Feature Tool Pack something something. And I want this server to be as clean as possible. But if someone tries, do tell if that works too!

Weird thing is, you can go look for these assemblies in your Program Files (x86)\EPiServer\CMS\7.5.394.2\Install\Modules\EPiServer Commerce 7.5.394.2\Binaries folder if you have installed Commerce via the Deployment Center. And you will find an assembly with the right name, but with version 10.0.40219.1, which really won't help you even the slightest.