EDIT: Solved! With thanks to Zenwaichi:
Go to your Apps folder (Windows 8/8.1):

   C:\Users\[computer account name]\AppData\Local\Apps

and delete everything (except things of which you can clearly tell what they're from and have nothing to do with KHUT). Download setup, install and launch KHUT.

Trainer version: Cannot access the trainer to check
OS:                      Windows 8.1
Browser:             Chrome (but I don't think that's relevant here)
Game:                 N/A

Issue: Trainer gives the following details of the error on launch (I hope you know Dutch):

       De volgende fouten zijn aangetroffen bij deze bewerking.     * [27-7-2016 09:43:48] System.ArgumentException         - De waarde valt niet binnen het verwachte bereik.         - Bron: System.Deployment         - Stack-tracering:             bij System.Deployment.Application.NativeMethods.CorLaunchApplication(UInt32 hostType, String applicationFullName, Int32 manifestPathsCount, String[] manifestPaths, Int32 activationDataCount, String[] activationData, PROCESS_INFORMATION processInformation)             bij System.Deployment.Application.ComponentStore.ActivateApplication(DefinitionAppId appId, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.SubscriptionStore.ActivateApplication(DefinitionAppId appId, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.ApplicationActivator.Activate(DefinitionAppId appId, AssemblyManifest appManifest, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.ApplicationActivator.ProcessOrFollowShortcut(String shortcutFile, String& errorPageUrl, TempFile& deployFile)             bij System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut, String textualSubId, String deploymentProviderUrlFromExtension, BrowserSettings browserSettings, String& errorPageUrl)             bij System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state)

Additionally, clicking "Uninstall" after selecting KHUT in Windows' regular program manager and CCleaner doesn't do anything./

Trying to reinstall nets me the same error:

    De volgende fouten zijn aangetroffen bij deze bewerking.     * [27-7-2016 09:47:19] System.ArgumentException         - De waarde valt niet binnen het verwachte bereik.         - Bron: System.Deployment         - Stack-tracering:             bij System.Deployment.Application.NativeMethods.CorLaunchApplication(UInt32 hostType, String applicationFullName, Int32 manifestPathsCount, String[] manifestPaths, Int32 activationDataCount, String[] activationData, PROCESS_INFORMATION processInformation)             bij System.Deployment.Application.ComponentStore.ActivateApplication(DefinitionAppId appId, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.SubscriptionStore.ActivateApplication(DefinitionAppId appId, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.ApplicationActivator.Activate(DefinitionAppId appId, AssemblyManifest appManifest, String activationParameter, Boolean useActivationParameter)             bij System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut, String textualSubId, String deploymentProviderUrlFromExtension, BrowserSettings browserSettings, String& errorPageUrl)             bij System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state)