These are the messages:

Started a transacted install

An error has occured and the transaction will be rolled back

Rolledback

Could not load type 'EPiServer.Events.EventsServiceKnownTypeAttribute' from assembly 'EPiServer.Events, Version=6.2.267.1, Culture=neutral, PublicKeyToken=8fe

83dea738b45b7'.

When executing

At C:\Program Files (x86)\EPiServer\RelatePlus\2.1.0.0\Install\Install EPiServer Relate.ps1:317 char:19

+ Add-EPiServerData <<<< $importSource $destinationFolder $applicationPath -updateStartPageAttribute
....

I can't find the EventsServiceKnownTypeAttribute in my ILSpy either.

OS: Win 7
Any advice or help is appreciated!

Can you check the file versions of EPiServer.Events as well as EPiServer.Common.* + EPiServer.Community.*?

It sounds to me like you have a mix of hotfixed and non-hotfixed versions of assemblies (non hotfixed EPiServer.Events but other assemblies depending on the hotfixed version?).

Yes, I wasn't aware of the hotfix(es).  

Events: 6.2.267.1

Common.*: All common modules except EPiServer.Common.ComponentArt.Web.UI are on 4.1.517.500

Community.*: 4.1.517.500 mostly, some on 4.1.517.358

Will applying hotfix 6.1.379.502 solve the problem?

Yes, the problem seems to be that you have the original version of the Events assembly together with versions of other assemblies that depend on the hotfixed version.

Ensuring you have the updated versions as listed on http://world.episerver.com/Articles/Items/About-the-Latest-Updates-for-EPiServer-CMS-and-Relate/ should fix the problem.

Unfortunately I get the exact same problem, and this time I've tested the site and get the same message:

 Could not load type 'EPiServer.Events.EventsServiceKnownTypeAttribute' from assembly 'EPiServer.Events, Version=6.2.267.1, Culture=neutral, PublicKeyToken=8fe83dea738b45b7'.

I followed the installation instruction of the 6.1.379.502 update. The only difference I can see is that Events.dll assembly file version  is on 6.2.267.500.

However, in my VS Object Browser I can see the the class:

public sealed class EventsServiceKnownTypeAttribute : System.Attribute
Member of EPiServer.Events

but it is not visible in ILspy.

This is the top of the stack trace when running the application:

[TypeLoadException: Could not load type 'EPiServer.Events.EventsServiceKnownTypeAttribute' from assembly 'EPiServer.Events, Version=6.2.267.1, Culture=neutral, PublicKeyToken=8fe83dea738b45b7'.]
System.ModuleHandle.ResolveType(Int32 typeToken, RuntimeTypeHandle* typeInstArgs, Int32 typeInstCount, RuntimeTypeHandle* methodInstArgs, Int32 methodInstCount) +0
System.ModuleHandle.ResolveTypeHandle(Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext) +227
System.Reflection.Module.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments) +355
System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, Module decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, RuntimeMethodHandle& ctor, Boolean& ctorHasParameters, Boolean& isVarArg) +474
System.Reflection.CustomAttribute.IsCustomAttributeDefined(Module decoratedModule, Int32 decoratedMetadataToken, RuntimeType attributeFilterType, Boolean mustBeInheritable) +630
System.Reflection.CustomAttribute.IsDefined(RuntimeType type, RuntimeType caType, Boolean inherit) +100
Microsoft.Internal.AttributeServices.IsAttributeDefined(ICustomAttributeProvider attributeProvider) +140

Hi Cristian,

Strange. .502 should have fixed that. I think we need to figure out where the episerver.events.dll is loaded from. Can you configure the fusion log to log all binds and restart the site and locate the log item for loading episerver.events.dll? We have heard of cases where you actually needed to clear the temporary aspnet files to have it regenerated with the updated assemblies.

I tested tho clear out the temporary-aspnet-files, but no change.
I'm not so familiar with fuslogvw but I collected the folloing entries when installing:

*** Assembly Binder Log Entry (2012-06-05 @ 09:46:11) ***
The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.
Assembly manager loaded from: C:\Windows\Microsoft.NET\Framework\v2.0.50727\mscorwks.dll
Running under executable C:\Program Files (x86)\EPiServer\Shared\Install\EPiServerInstall.exe

When executing I got

*** Assembly Binder Log Entry (2012-06-05 @ 09:28:30) ***
The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.
Assembly manager loaded from: C:\Windows\Microsoft.NET\Framework64\v2.0.50727\mscorwks.dl

Running under executable C:\Windows\system32\inetsrv\InetMgr.exe

I notice that the Framework is 64-bit when running, but not when installing. Maybe something is in error in the op and/or that I should reinstall EPiServer with the installation program or try on another environment? I have no problem installing a new CMS-site, however when installing the Alloy tech additional I get a similar problem. EPiServer.Personalization.VisitorGroups.VisitorGroupValidation.Validate is claimed to be missing. This seems to be a result from changes in the latest release, since I have installed this successfully on this computer quite recently.

It's working! My colleague pointed out that the file version in the Version-tab of the Episerver.events' properties in the GAC was still the old one. So the file version was still the old wan in the GAC. We then re-installed the EPiServer.Framework msi, and this time the GAC file version DID change! And I have no explanation whatsoever why this didn't happen the first time. I haven't checked all the other libraries, so the problem with Alloy-templates not being loaded may still remain, but I am hopeful.

Thanks for all help!