We might get the below error while trying to register a plugin.

Cause –

The plugin project was referring the .NET Framework 4.7.2

And the latest version of Microsoft.CrmSdk.CoreAssemblies – (Sept 29, 2020)

Resolution –

Changing it to 4.6.2 fixed it.

Details-

Unhandled Exception: System.ServiceModel.FaultException

An unexpected error occurred.

Server stack trace:

at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)

at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)

at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)

at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [0]:

at Microsoft.Xrm.Tooling.Connector.CrmServiceClient.Create(Entity entity)

at Xrm.Sdk.PluginRegistration.Forms.PluginRegistrationForm.btnRegister_Click(Object sender, EventArgs e)

Detail:

<OrganizationServiceFault xmlns=”http://schemas.microsoft.com/xrm/2011/Contracts&#8221; xmlns:i=”http://www.w3.org/2001/XMLSchema-instance”&gt;

<ActivityId>6906e911-4a07-487a-bdf0-ad52914b9f14</ActivityId>

<ErrorCode>-2147220970</ErrorCode>

<ErrorDetails xmlns:a=”http://schemas.datacontract.org/2004/07/System.Collections.Generic”&gt;

<KeyValuePairOfstringanyType>

<a:key>ApiExceptionSourceKey</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>Plugin/Microsoft.Crm.ObjectModel.PluginAssemblyService</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiOriginalExceptionKey</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>Microsoft.Crm.CrmException: An unexpected error occurred. —&gt; System.FormatException: Input string was not in a correct format.

at System.Text.StringBuilder.FormatError()

at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)

at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)

at System.String.Format(IFormatProvider provider, String format, Object arg0, Object arg1)

at Microsoft.Crm.ObjectModel.TargetFrameworkVersionValidator.ValidateInternal()

at Microsoft.Crm.ObjectModel.PluginValidatorBase.Validate()

at Microsoft.Crm.ObjectModel.PluginAssemblyServiceInternal`1.ValidateAssemblyMetadata(ExecutionContext context, IBusinessEntity pluginAssembly, CrmPluginAssemblyMetadata assemblyMetadata)

at Microsoft.Crm.ObjectModel.PluginAssemblyServiceInternal`1.VerifyRegistrationAbility(IBusinessEntity pluginAssembly, Boolean createCall, ExecutionContext context, CrmPluginAssemblyMetadata assemblyMetadata)

at Microsoft.Crm.ObjectModel.PluginAssemblyServiceInternal`1.ValidateOperation(String operationName, IBusinessEntity entity, ExecutionContext context)

at Microsoft.Crm.ObjectModel.SdkEntityServiceBase.CreateInternal(IBusinessEntity entity, ExecutionContext context, Boolean verifyAction)

— End of inner exception stack trace —

at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context)

at Microsoft.Crm.Extensibility.PipelineInstrumentationHelper.Execute(Boolean instrumentationEnabled, String stopwatchName, ExecuteWithInstrumentation action, PipelineExecutionContext context)

at Microsoft.Crm.Extensibility.Pipeline.&lt;&gt;c__DisplayClass5_0.&lt;RunStep&gt;b__0()</a:value>

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiStepKey</a:key>

<a:value i:type=”b:guid” xmlns:b=”http://schemas.microsoft.com/2003/10/Serialization/”>3ecabb1b-ea3e-db11-86a7-000a3a5473e8</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiDepthKey</a:key>

<a:value i:type=”b:int” xmlns:b=”http://www.w3.org/2001/XMLSchema”>1</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiActivityIdKey</a:key>

<a:value i:type=”b:guid” xmlns:b=”http://schemas.microsoft.com/2003/10/Serialization/”>6906e911-4a07-487a-bdf0-ad52914b9f14</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiPluginSolutionNameKey</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>System</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiStepSolutionNameKey</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>System</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiExceptionCategory</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>SystemFailure</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiExceptionMesageName</a:key>

<a:value i:type=”b:string” xmlns:b=”http://www.w3.org/2001/XMLSchema”>UnExpected</a:value&gt;

</KeyValuePairOfstringanyType>

<KeyValuePairOfstringanyType>

<a:key>ApiExceptionHttpStatusCode</a:key>

<a:value i:type=”b:int” xmlns:b=”http://www.w3.org/2001/XMLSchema”>400</a:value&gt;

</KeyValuePairOfstringanyType>

</ErrorDetails>

Hope it helps..