Could not load file or assembly in reporting services - reporting-services

Question

I've created one project for report localization, which consists one class file and three .resx files. In class file, I wrote code which find appropriate .resx file, depending on culture, and read value for given key.
After that, i build up project, copy the .dll into "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies" and change RSPreviewPolicy.config, where I've added one new PermissionSet for Report localization and one CodeGroup tag giving Permission to .dll.
Next step I did was creating report, referencing .dll and write one expression to test localization.
I got following error:
"Failed to load expression host assembly. Details: Could not load file or assembly
I'm obviously missing something, but I can't figure out what?
Does somebody has idea of what to do?

Answer 1

I've found the answer. Problem were permissions for viewing report in Visual Studio Preview mode.
First of all, I was putting dll (with localization class) into next location:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies.
After that, I needed to change RSPreviewPolicy.config file, that exists in same folder location, to apply some security permissions.
In question, I mentioned that I've added one PermisionSet, but now I am sure there is no need for that.
I've just changed two CodeGroup section, which have Execution permission level, to have FullTrust permission level, like this:
<CodeGroup
class="UnionCodeGroup"
version="1"
PermissionSetName="FullTrust"
Name="Report_Expressions_Default_Permissions"
Description="This code group grants default permissions for code in report expressions and Code element. ">
.
.
.
</CodeGroup>
<CodeGroup
class="FirstMatchCodeGroup"
version="1"
PermissionSetName="FullTrust"
Description="This code group grants MyComputer code Execution permission. ">
.
.
.
</CodeGroup>
Regarding your version of Visual Studio, you must choose appropriate folder path:
for VS 2015 --- C:\Program Files (x86)\Microsoft Visual Studio
14.0\Common7\IDE\PrivateAssemblies
for VS 2013 --- C:\Program Files (x86)\Microsoft Visual Studio
12.0\Common7\IDE\PrivateAssemblies
for VS 2010 --- C:\Program Files (x86)\Microsoft Visual Studio
10.0\Common7\IDE\PrivateAssemblies