I do not have .NET 2.0 or 3.5 installed, only 4.5. Could that be the reason for hanging?

From nunit-gui_3304.log:
InternalTrace: Initializing at level Verbose
17:00:00.019 Info  [ 1] AppEntry: Starting NUnit GUI
17:00:00.019 Info  [ 1] AppEntry: Adding Services
17:00:00.019 Debug [ 1] ServiceManager: Added SettingsService
17:00:00.019 Debug [ 1] ServiceManager: Added DomainManager
17:00:00.019 Debug [ 1] ServiceManager: Request for service ISettings satisfied by SettingsService
17:00:00.019 Debug [ 1] ServiceManager: Added RecentFilesService
17:00:00.019 Debug [ 1] ServiceManager: Added ProjectService
17:00:00.035 Debug [ 1] ServiceManager: Added TestLoader
17:00:00.035 Debug [ 1] ServiceManager: Added AddinRegistry
17:00:00.035 Debug [ 1] ServiceManager: Added AddinManager
17:00:00.035 Debug [ 1] ServiceManager: Added TestAgency
17:00:00.035 Info  [ 1] AppEntry: Initializing Services
17:00:00.035 Info  [ 1] ServiceManager: Initializing SettingsService
17:00:00.035 Info  [ 1] ServiceManager: Initializing DomainManager
17:00:00.035 Info  [ 1] ServiceManager: Initializing RecentFilesService
17:00:00.035 Info  [ 1] ServiceManager: Initializing ProjectService
17:00:00.035 Info  [ 1] ServiceManager: Initializing TestLoader
17:00:00.035 Info  [ 1] ServiceManager: Initializing AddinRegistry
17:00:00.035 Info  [ 1] ServiceManager: Initializing AddinManager
17:00:00.035 Debug [ 1] ServiceManager: Request for service IAddinRegistry satisfied by AddinRegistry
17:00:00.035 Info  [ 1] ServiceManager: Initializing TestAgency
17:00:00.097 Info  [ 1] AppEntry: Initializing AmbientProperties
17:00:00.097 Info  [ 1] AppEntry: Constructing Form
17:00:00.331 Debug [ 1] ServiceManager: Request for service RecentFiles satisfied by RecentFilesService
17:00:00.331 Debug [ 1] ServiceManager: Request for service TestLoader satisfied by TestLoader
17:00:00.331 Info  [ 1] AppEntry: Starting Gui Application
17:00:00.378 Debug [ 1] ResultTabs: Updating tab pages
17:00:00.472 Info  [ 1] TestLoader: Loading project C:\ObfuscatedPath\TestHPC.dll, default config
17:00:00.472 Debug [ 1] ServiceManager: Request for service ProjectService satisfied by ProjectService
17:00:00.487 Info  [ 1] TestLoader: Loading tests for TestHPC.dll
17:00:00.503 Debug [ 1] RuntimeFrameworkSelector: Current framework is net-3.5
17:00:00.503 Debug [ 1] RuntimeFrameworkSelector: No specific framework requested
17:00:00.518 Debug [ 1] RuntimeFrameworkSelector: Assembly C:\ObfuscatedPath\TestHPC.dll uses version 4.0.30319
17:00:00.518 Debug [ 1] ServiceManager: Request for service TestAgency satisfied by TestAgency
17:00:00.518 Debug [ 1] RuntimeFrameworkSelector: Test will use net-4.0 framework
17:00:00.534 Info  [ 1] ProcessRunner: Loading TestHPC.dll
17:00:00.534 Info  [ 1] TestAgency: Getting agent for use under net-4.0
17:00:00.534 Debug [ 1] TestAgency: Using nunit-agent at C:\ObfuscatedPathToNUnit\NUnit\NUnit-2.6.2.12296\bin\nunit-agent.exe
17:00:00.534 Info  [ 1] TestAgency: Launched Agent process 6900 - see nunit-agent_6900.log
17:00:00.534 Info  [ 1] TestAgency: Command line: "C:\ObfuscatedPathToNUnit\NUnit\NUnit-2.6.2.12296\bin\nunit-agent.exe" 86f6d784-98e9-4744-b49b-3cdb45ed7cd2 tcp://127.0.0.1:64997/TestAgency
17:00:00.534 Debug [ 1] TestAgency: Waiting for agent {86f6d784-98e9-4744-b49b-3cdb45ed7cd2} to register
17:00:00.940 Debug [ 1] TestAgency: Returning new agent {86f6d784-98e9-4744-b49b-3cdb45ed7cd2}
17:00:01.470 Info  [ 1] AssemblyWatcher: FreeResources
17:00:01.470 Info  [ 1] AssemblyWatcher: Setting up watcher
17:00:01.470 Debug [ 1] AssemblyWatcher: Setting up FileSystemWatcher for C:\ObfuscatedPath\TestHPC.dll
17:00:01.501 Debug [ 1] TestSuiteTreeView: Added to map: [0-1003]C:\ObfuscatedPath\TestHPC.dll
17:00:01.501 Debug [ 1] TestSuiteTreeView: Added to map: [0-1004]TestHPC
17:00:01.501 Debug [ 1] TestSuiteTreeView: Added to map: [0-1000]TestHPC.TestHpc
17:00:01.501 Debug [ 1] TestSuiteTreeView: Added to map: [0-1001]TestHPC.TestHpc.AllCoresPresent
17:00:01.501 Debug [ 1] TestSuiteTreeView: Added to map: [0-1002]TestHPC.TestHpc.AllCoresPresent("HPC-HEAD-DEV",9)
17:00:16.836 Info  [ 1] TestLoader: Reloading tests for TestHPC.dll
17:00:16.851 Info  [ 1] AssemblyWatcher: FreeResources
17:00:16.851 Info  [ 1] ProcessRunner: Unloading TestHPC.dll
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Current framework is net-3.5
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: No specific framework requested
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Assembly C:\ObfuscatedPath\TestHPC.dll uses version 4.0.30319
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Test will use net-4.0 framework
17:00:16.867 Info  [ 1] ProcessRunner: Stopping remote agent
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Current framework is net-3.5
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Requested framework is net-4.0
17:00:16.867 Debug [ 1] RuntimeFrameworkSelector: Test will use net-4.0 framework
17:00:16.867 Info  [ 1] ProcessRunner: Loading TestHPC.dll
17:00:16.867 Info  [ 1] TestAgency: Getting agent for use under net-4.0
17:00:16.867 Debug [ 1] TestAgency: Using nunit-agent at C:\ObfuscatedPathToNUnit\NUnit\NUnit-2.6.2.12296\bin\nunit-agent.exe
17:00:16.867 Info  [ 1] TestAgency: Launched Agent process 7248 - see nunit-agent_7248.log
17:00:16.867 Info  [ 1] TestAgency: Command line: "C:\ObfuscatedPathToNUnit\NUnit\NUnit-2.6.2.12296\bin\nunit-agent.exe" 98a4cd49-4536-45b7-8833-8ad123680fe4 tcp://127.0.0.1:64997/TestAgency
17:00:16.867 Debug [ 1] TestAgency: Waiting for agent {98a4cd49-4536-45b7-8833-8ad123680fe4} to register
17:00:17.070 Debug [ 1] TestAgency: Returning new agent {98a4cd49-4536-45b7-8833-8ad123680fe4}
17:00:17.616 Info  [ 1] AssemblyWatcher: FreeResources
17:00:17.616 Info  [ 1] AssemblyWatcher: Setting up watcher
17:00:17.616 Debug [ 1] AssemblyWatcher: Setting up FileSystemWatcher for C:\ObfuscatedPath\TestHPC.dll
17:00:17.631 Debug [ 1] TestSuiteTreeView: Added to map: [0-1003]C:\ObfuscatedPath\TestHPC.dll
17:00:17.631 Debug [ 1] TestSuiteTreeView: Added to map: [0-1004]TestHPC
17:00:17.631 Debug [ 1] TestSuiteTreeView: Added to map: [0-1000]TestHPC.TestHpc
17:00:17.631 Debug [ 1] TestSuiteTreeView: Added to map: [0-1001]TestHPC.TestHpc.ObfuscatedTestName
17:00:17.631 Debug [ 1] TestSuiteTreeView: Added to map: [0-1002]TestHPC.TestHpc.ObfuscatedTestName("OBFUSCATED",9)
17:00:17.647 Info  [ 1] TestLoader: Reload complete
17:00:18.131 Debug [ 6] TestLoader: Got RunStarted Event