The first thing you could check, is that the virtual paths are set up correctly in web.config. Util, App_Themes_Default, WebServices and YourCustomEditAdminPath should be mapped to "C:\Program Files\EPiServer\CMS\5.2.375.7\xxx" 

I haven't tried this on an R2 SP1 site yet, but when R2 first came out, we had problems installing sites on a different drive than the C-drive. Our workaround was to install the site on the C-drive and then move it to the other drive. 

Not sure if this is your problem, but the error message indicates that there are something wrong with your vpp folders...

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Lars Øyvind Bodahl 

Hello! And thx for reply!!!       

I checked the paths and they seem ok to me. On 64bit the appfiles are located in Program Files (x86) but that is reflected in web.config also...:

        <add name="App_Themes_Default" virtualPath="~/App_Themes/Default/" physicalPath="C:\Program Files (x86)\EPiServer\CMS\5.2.375.133\application\App_Themes\Default" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider,EPiServer" />
        <add name="UI" virtualPath="~/SEC/" physicalPath="C:\Program Files (x86)\EPiServer\CMS\5.2.375.133\application\UI" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider,EPiServer" />
        <add name="UtilFiles" virtualPath="~/Util/" physicalPath="C:\Program Files (x86)\EPiServer\CMS\5.2.375.133\application\util" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider,EPiServer" />
        <add name="WebServiceFiles" virtualPath="~/WebServices/" physicalPath="C:\Program Files (x86)\EPiServer\CMS\5.2.375.133\application\webservices" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider,EPiServer" />

The message I  get after logging in to the Edit-mode is: 

Install Basic Content  
Some basic content is needed in order to start using EPiServer CMS. Select one of the options below, a system language and click Finish.
 No import package folder was passed via querystring parameter
The ~/util/setup folder does not contain any packages
The manager's modules folder does not contain any packages [C:\Program Files\EPiServer\Manager\Modules] 

 Anyone have a solution to this? Am I doing something wrong?

There is a long story behind this behaviour, I won't go into that now. 

The redirect only happens when pageStartId does not contain a valid value, so set pageStartId in web.config to 1 or something and you should be good to go.