1) Did you notice any red error messages during the upgrade?
2) Please confirm that the site's server had ASP.Net 3.5 SP1 installed prior to the upgrade as this is a now a requirement
3) Please confirm that about 1/3 of the way down in the site's web.config file, you see the following assembly nodes (note Version=3.5.0.0):
<add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
<add assembly="System.Data.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
4) Please confirm that near the top of the web.config file you have the following section nodes:
<section name="moduleCaching" requirePermission="false" type="DotNetNuke.Framework.Providers.ProviderConfigurationHandler, DotNetNuke" />
<section name="outputCaching" requirePermission="false" type="DotNetNuke.Framework.Providers.ProviderConfigurationHandler, DotNetNuke" />
5) Please confirm that near the bottom of the web.,config file you have the following provider nodes:
<moduleCaching defaultProvider="FileModuleCachingProvider">
<providers>
<clear />
<add name="FileModuleCachingProvider" type="DotNetNuke.Services.ModuleCache.FileProvider, DotNetNuke.Provider.ModuleCaching.FileProvider" providerPath="~\Providers\ModuleCachingProviders\FileModuleCachingProvider\" />
<add name="MemoryModuleCachingProvider" type="DotNetNuke.Services.ModuleCache.MemoryProvider, DotNetNuke.Provider.ModuleCaching.MemoryProvider" providerPath="~\Providers\ModuleCachingProviders\MemoryModuleCachingProvider\" />
</providers>
</moduleCaching>
<outputCaching defaultProvider="FileOutputCachingProvider">
<providers>
<clear />
</providers>
</outputCaching>