转载注意：本文由思想瞭望者首发于博客园，转载请注明出处。
本文参考了：
- https://forum.uipath.com/t/access-denied-to-launch-an-application-when-running-uipath/220677/2
- https://forum.uipath.com/t/access-denied-1/236092/10
因此解决方案并非本人原创。本人仅作搬运工作。
现象
在UiPath Studio中Debug或者Run任意Workflow时（即使是新建的空的Workflow），无法启动并立即报错，提示类似以下消息：
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20.4.2
拒绝访问。
RemoteException wrapping System.ComponentModel.Win32Exception: 拒绝访问。
at System.Diagnostics.ProcessManager.OpenProcess(Int32 processId, Int32 access, Boolean throwIfExited)
at System.Diagnostics.Process.GetProcessHandle(Int32 access, Boolean throwIfExited)
at System.Diagnostics.Process.OpenProcessHandle(Int32 access)
at System.Diagnostics.Process.set_EnableRaisingEvents(Boolean value)
at UiPath.Service.UserHost.AttendedServiceProxy.RegisterClientProcess(Int32 clientPid)
at UiPath.Service.UserHost.StudioOperations.<Prepare>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.Service.Core.Utils.TaskUtils.<WithShortWait>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.Service.UserHost.StudioOperations.<>c__DisplayClass5_0.<<RunJob>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.CancellationHelper`1.<Invoke>d__3`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.Server.<InvokeMethod>d__22.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.Server.<HandleRequest>d__21.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.Server.<>c__DisplayClass4_2.<<-ctor>b__6>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.IOHelpers.<WithResult>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at UiPath.CoreIpc.IOHelpers.<WithTimeout>d__16`1.MoveNext()
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此时，在计算机管理的事件查看器中，应用程序日志可以看到这样一条错误（如下图）。
本机同时装有的其它RPA工具上并未发生此现象。
原因
暂不明确。但可以确定问题出在UiPath本身，而不是系统环境。
解决方案
在任务管理器中，在“详细信息”页面，选中“UiPath.Service.UserHost.exe”，然后结束任务。即可正常运行。亲测有效。
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