I recently updated to Trados Studio 2021 CU8 (version 16.1.8.4404) and Studio no longer opened. It got as far as "Loading Plugins", then just shut down. It didn't display any errors. I've rebooted several times, I've uninstalled and reinstalled it several times, I've tried the usual resetting fixes of renaming the Studio 2021 folder in Documents and the numbered folders in C:\Users\[User]\AppData\Roaming\SDL to something with _old on the end and restarting, but nothing is working. I kept the installer for my previous build (16.1.6.4276) and have reinstalled that, and that still works.

When I tried to open the new version, the log it generated showed:

FATAL [2021-07-07 22:27:26,011] Sdl.Desktop.Platform.UnhandledException - An unexpected error has occurred while loading the application plug-ins. System.IO.FileFormatException: File contains corrupted data. at MS.Internal.IO.Zip.ZipIOEndOfCentralDirectoryBlock.FindPosition(Stream archiveStream) at MS.Internal.IO.Zip.ZipIOEndOfCentralDirectoryBlock.SeekableLoad(ZipIOBlockManager blockManager) at MS.Internal.IO.Zip.ZipArchive..ctor(Stream archiveStream, FileMode mode, FileAccess access, Boolean streaming, Boolean ownStream) at MS.Internal.IO.Zip.ZipArchive.OpenOnFile(String path, FileMode mode, FileAccess access, FileShare share, Boolean streaming) at System.IO.Packaging.ZipPackage..ctor(String path, FileMode mode, FileAccess access, FileShare share, Boolean streaming) at System.IO.Packaging.Package.Open(String path, FileMode packageMode, FileAccess packageAccess, FileShare packageShare, Boolean streaming) at System.IO.Packaging.Package.Open(String path, FileMode packageMode, FileAccess packageAccess) at Sdl.Core.PluginFramework.PackageSupport.PluginPackage.OpenPackage(FileAccess fileAccess) at Sdl.Core.PluginFramework.PackageSupport.ThirdPartyPluginLocator.SyncPlugInPackages(String thirdPartyPluginsDirectory, String thirdPartyPluginsPackagesDirectory) at Sdl.Core.PluginFramework.PackageSupport.ThirdPartyPluginLocator.SyncPlugInPackages() at Sdl.Core.PluginFramework.PackageSupport.ThirdPartyPluginLocator.GetPluginDescriptors() at Sdl.Core.PluginFramework.PackageSupport.ValidatingThirdPartyPluginLocator.ValidateThirdPartyPluginDescriptors(IFrameworkConfiguration configuration) at Sdl.Core.PluginFramework.PackageSupport.ValidatingThirdPartyPluginLocator..ctor(IPluginLocator baseLocator, IFrameworkConfiguration configuration, Boolean isSecureMode) at Sdl.Desktop.Platform.PluginManagement.PluginRegistryBuilder.BuildThirdPartyLocator(Boolean loadThirdPartyPlugins, Boolean isSecureMode, String configPath) at Sdl.Desktop.Platform.PluginManagement.PluginLoaderService.LoadPlugins(Boolean loadThirdPartyPlugins, Boolean isSecureMode, IFunctionalityFilter functionalityFilter) INFO [2021-07-07 22:27:26,322] Sdl.Desktop.Platform.UnhandledException - An unexpected error has occurred while loading the application plug-ins.#ProcessName=SDLTradosStudio#PhysicalMemorySize=82886656#VirtualMemorySize=49786880#ThreadCount=24#HandleCount=824#GdiHandleCount=47#UserHandleCount=36#TotalProcessorTime=00:00:12.1875000 INFO [2021-07-07 22:27:27,450] Sdl.Desktop.Platform.Implementation.Services.UpdateService - Started TrueUpdate Process Id: 23664 INFO [2021-07-07 22:28:04,891] Sdl.Desktop.Platform.Implementation.Services.UpdateService - TrueUpdate Process Id: 23664has exited INFO [2021-07-07 22:28:04,894] Sdl.Desktop.Platform.Implementation.Services.UpdateService - Trying to read file:C:\Users\User\AppData\Local\Temp\Studio16Updates\FilteredUpdates.xml INFO [2021-07-07 22:28:04,897] Sdl.Desktop.Platform.Implementation.Services.UpdateService - File not found

The FilteredUpdates.xml file was indeed missing. I had tried installing the WorldServer Compatibility Pack, which apparently should have fixed any errors, but it didn't help. I uninstalled the WorldServer pack, reinstalled the previous version of Studio, and the file exists again now and everything is working - but I can't get the CU8 update to work!