Not all NUnit unit tests are running-Getting an exception

Running Nunit test from Resharper\UnitTests\RunUnitTests

after running few unit test it throws below error.

2017.10.09 10:28:39.146 ERROR System.InvalidCastException: Unable to cast object of type 'JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTestTask' to type 'JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTestFixtureTask'.
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.PrepareFixturesAndTests(TaskExecutionNode assemblyNode, String assemblyLocation)
at JetBrains.ReSharper.UnitTestRunner.nUnit.NUnitTaskRunner.ExecuteRecursive(TaskExecutionNode node)
at JetBrains.ReSharper.TaskRunnerFramework.StartupTaskRunnerHost.Execute(TaskExecutionNode node)
at JetBrains.ReSharper.TaskRunnerFramework.StartupTaskRunnerHost.ExecuteNodes(IEnumerable`1 nodes)
at JetBrains.ReSharper.TaskRunnerFramework.TasksPacketHandler.ThreadProc(TaskRunnerProxy proxy, IEnumerable`1 packets, AssemblyLoader loader)