This is related to the episerver.shell/modules section in web.config (see sample config below). Do you have any gadgets in your solution? 

 <episerver.shell>
    <publicModules rootPath="~/modules/" autoDiscovery="Modules" />
    <protectedModules rootPath="~/episerver/">
    </protectedModules>
  </episerver.shell>

I had the same problem - I had a gadget registered under publicModules. I removed the registration before running the VPP migration tool, and then added it back after VPP migration.

Have anyone used the VPP migration tool successfully with the new version of EPI? (7.5.1000.0/7.5.446.0)

It just crashes for me.

Thanks for all the answers!

my episerver.shell looks like this:

<episerver.shell>
<publicModules rootPath="~/modules/" autoDiscovery="Modules">

     <add name="SLSO">
          <assemblies>
               <add assembly="SLSO" />
          </assemblies>
     </add>
</publicModules>

<protectedModules rootPath="~/test/ui/">
     <add name="Find">
          <assemblies>
               <add assembly="EPiServer.Find.Framework" />
               <add assembly="EPiServer.Find.Cms" />
          </assemblies>
     </add>
</protectedModules>
</episerver.shell>

If i remove the <add name="SLSO">-section and/or <add name="Find">-section the site won't start. Mari, is it ok to run the tool on the site when it is'nt working correctly? :).

Ok so I did screw up when migrating my settings from the old configs to the new-ones.

I changed the: <protectedModules rootPath="~/test/ui/"> to <protectedModules rootPath="~/episerver/"> and now the Connect-button gives me this message:

Cannot find any virtual path providers to migrate.

You should only need  to remove the SLSO one, under public modules. The site should run even if you remove it. If it fails, then there is something else wrong.

If it says it can't fin any vpp's to migrate then you need to check your episerverframework.config - have you got the VPPs listed?

Ok, so I removed the:

<add name="SLSO">
<assemblies>
<add assembly="SLSO" />
</assemblies>
</add>

and returned some old code from episerverframework again and now it loads! :D

Mari you are an angel!

Niklas Wanngren: try to check in your windows log to see why the application crashes.

Ok so now I get the next error then I press Migrate:

Content with id 162 was not found
at EPiServer.DataFactory.Get[T](ContentReference contentLink, ILanguageSelector languageSelector)
at EPiServer.Core.ContentLanguageSettingsHandler.GetClosestSettingNoCache(ContentReference contentLink, Dictionary`2 allSettings)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at EPiServer.Core.ContentLanguageSettingsHandler.GetClosestSetting(ContentReference contentLink)
at EPiServer.Core.ContentLanguageSettingsHandler.Get(ContentReference contentLink)
at EPiServer.Core.ContentLanguageSettingsHandler.Get(ContentReference contentLink, String languageBranch)
at EPiServer.Core.LanguageSelector.LoadLanguage(LanguageSelectorContext context)
at EPiServer.Core.ContentProvider.LoadChildren[T](ContentReference contentLink, ILanguageSelector selector, Int32 startIndex, Int32 maxRows)
at EPiServer.DataFactory.GetChildren[T](ContentReference contentLink, ILanguageSelector selector, Int32 startIndex, Int32 maxRows)
at EPiServer.DataFactory.GetChildren[T](ContentReference contentLink, ILanguageSelector selector)
at EPiServer.DataFactory.GetChildren[T](ContentReference contentLink)
at VppMigrationTool.Util.VppConverter.RebuildUrlSegment(ContentReference contentLink) in d:\Builds\132\EPiServerCMS Modules\VppMigrationTool\Sources\C\TFS\VppMigrationTool\Util\VppConverter.cs:line 154
at VppMigrationTool.Util.VppConverter.Convert() in d:\Builds\132\EPiServerCMS Modules\VppMigrationTool\Sources\C\TFS\VppMigrationTool\Util\VppConverter.cs:line 55
Done
Directories: 0
Files: 0
ContentFolders: 0
FileContent: 0
Blobs: 0

Thanks Mari, you made my day. I had registered a plug in. Removing the registration in web.config made the error go away:

<episerver.shell>
	<publicModules rootPath="~/modules/" autoDiscovery="Modules">
		<add name="X">
			<assemblies>
				<add assembly="X" />
			</assemblies>
		</add>
	</publicModules>
	<protectedModules rootPath="~/EPiServer/" />
</episerver.shell>