Unable to find Assembly error when using <codeSubDirectories> in web.config

I have a web site that uses the both c# and vb.net in the app_code section. The different languages are separated into their own folder and correctly configured in the web.config.

<codeSubDirectories>
    <add directoryName="BasicCode"/>
    <add dir开发者_运维问答ectoryName="CSharpCode"/>
  </codeSubDirectories>

This works fine 95% of the time. In production using 2 load balanced servers I sporadically receive an error message along the lines of:

"Unable to find assembly 'App_SubCode_BasicCode.xxx, Version=0.0.0.0, Culture=netural, PublicKeyToken=null'.

The site is hosted in IIS7 and I think it has something to do with the name of the dll assigned during dynamic compilation. I do not see this problem in a single server environment. Could this be because when the session is balanced to the second server the dynamic compiled dll name is different?

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It's entirely possible that the two different servers are generating different names for the dynamic assemblies; in fact I think that's probably a dead cert.

The question, however, is why is one server producing an assembly name that the other one is then trying to use? With a bog standard load balanced Asp.Net site you'd never see this.

Are there any types defined in the website code that then get serialised (either to viewstate or to a shared session state)?

If so, then this could be the problem - one server dehydrates an object from one dynamic assembly, and the other tries and fails to hydrate it because it's version is a different name.

That said, I think I'd expect to see a TypeLoadException rather than one relating to Assembly Loading if that were the case.