Can't open package (オブジェクト参照がオブジェクト インスタンスに設定されていません。(System.NullReferenceException))

Hi!

I get the message "オブジェクト参照がオブジェクト インスタンスに設定されていません。" (System.NullReferenceException) when I try to open a package.

I'm trying to open a package sent from a new client.
Packages from other clients open without any problem.

Can anyone please tell me what I'm doing wrong.
I'm new at using Trados Studio so I'm afraid that I might be missing something very obvious.

Thank you in advance!

The error message is:

<?xml version="1.0"?>
-<SDLErrorDetails time="2018/07/15 0:38:09">
<ErrorMessage>オブジェクト参照がオブジェクト インスタンスに設定されていません。</ErrorMessage>

-<Exception>
<Type>System.NullReferenceException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</Type>
<HelpLink/>
<Source>Sdl.ProjectApi.Implementation</Source>
<HResult>-2147467261</HResult>

-<StackTrace>
-<![CDATA[   場所 Sdl.ProjectApi.Implementation.Project.AddAutomaticTaskHistory(IAutomaticTask task)
   場所 Sdl.ProjectApi.Implementation.Project.CopyAutomaticTaskHistory(IManualTask orginalManualTask, IEnumerable`1 automaticTasks, List`1 files)
   場所 Sdl.ProjectApi.Implementation.Project.CopyTasksHistory(IManualTask orginalManualTask, IProject project, List`1 files)
   場所 Sdl.ProjectApi.Implementation.Project.AddManualTask(IManualTask task, ITaskFile[] taskFiles, IUser assignTo, IPackageOperationMessageReporter messageReporter)
   場所 Sdl.ProjectApi.Implementation.ProjectPackageImport.ImportPackageProject(IPackageProject packageProject, Boolean& isNewProject)
   場所 Sdl.ProjectApi.Implementation.ProjectPackageImport.StartImpl()
   場所 Sdl.ProjectApi.Implementation.PackageOperation.Start()]]>
</StackTrace>
</Exception>

-<Environment>
<ProductName>SDL Trados Studio</ProductName>
<ProductVersion>14.0.0.0</ProductVersion>
<EntryAssemblyFileVersion>14.1.10011.20356</EntryAssemblyFileVersion>
<OperatingSystem>Microsoft Windows 10 Pro</OperatingSystem>
<ServicePack>NULL</ServicePack>
<OperatingSystemLanguage>1041</OperatingSystemLanguage>
<CodePage>932</CodePage>
<LoggedOnUser>DESKTOP-4KSF4K3\educt</LoggedOnUser>
<DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>
<ComputerName>DESKTOP-4KSF4K3</ComputerName>
<ConnectedToNetwork>True</ConnectedToNetwork>
<PhysicalMemory>16700484 MB</PhysicalMemory>
</Environment>
</SDLErrorDetails>