I'am upgrading from CMS 11 to CMS 12. And i get this error either at startup or when running the command 

dotnet-episerver update-database MyProject.csproj

with an existing database (CMS 11 database):

The operation failed because an index or statistics with name 'IDX_tblContentLanguage_fkLanguageBranchID' already exists on table 'dbo.tblContentLanguage'.
dotnet-episerver : Unhandled exception: Microsoft.Data.SqlClient.SqlException (0x80131904): The operation failed because an index or statistics with name 'IDX_tblContentLanguage_fkLanguageBranchID' already exists on table 'dbo.tblContentLanguage'.
At line:1 char:1
+ dotnet-episerver update-database MyProject.csproj
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (Unhandled excep...ntentLanguage'.:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError
 
   at Microsoft.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at Microsoft.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean isAsync, Int32 timeout, Boolean asyncWrite)
   at Microsoft.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, Boolean sendToPipe, Int32 timeout, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry, String methodName)
   at Microsoft.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at EPiServer.Net.Cli.ScriptRunner.<>c__DisplayClass5_0.<ExecuteScript>b__0() in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\ScriptRunner.cs:line 55
   at EPiServer.Net.Cli.DatabaseHandler.Execute[T](Func`1 f, Boolean commit) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\DatabaseHandler.cs:line 95
   at EPiServer.Net.Cli.ScriptRunner.ExecuteScript(StreamReader stream) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\ScriptRunner.cs:line 53
   at EPiServer.Net.Cli.ScriptRunner.ExecuteScripts(IEnumerable`1 files, Boolean requiresValidation) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\ScriptRunner.cs:line 97
   at EPiServer.Net.Cli.ScriptRunner.Execute(IEnumerable`1 files, Boolean requiresValidation) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\ScriptRunner.cs:line 29
   at EPiServer.Net.Cli.Commands.UpdateDatabase.RunAsync(CancellationToken token) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\Commands\UpdateDatabase.cs:line 127
   at EPiServer.Net.Cli.Commands.UpdateDatabase.StartAsync(CancellationToken cancellationToken) in E:\BuildAgent\work\e72ed2d7d1e92bba\src\EPiServer.Net.Cli\Commands\UpdateDatabase.cs:line 63
   at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at System.CommandLine.Invocation.CommandHandler.GetResultCodeAsync(Object value, InvocationContext context)
   at System.CommandLine.Invocation.ModelBindingCommandHandler.InvokeAsync(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.<>c__DisplayClass4_0.<<BuildInvocationChain>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseParseErrorReporting>b__21_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass16_0.<<UseHelp>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass25_0.<<UseVersionOption>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass23_0.<<UseTypoCorrections>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseSuggestDirective>b__22_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseParseDirective>b__20_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseDebugDirective>b__11_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<RegisterWithDotnetSuggest>b__10_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass14_0.<<UseExceptionHandler>b__0>d.MoveNext()

Are there any solution to fixing this error