System.MissingMethodException: Method not found: '!!0[] System.Array.Empty()'.

Hi,

Currently I am working in Dynamics 365. I created a plugin and uploaded for lead(Post Operation). when I tried created the lead it shows Two types of exceptions

1. System.MissingMethodException: Method not found: '!!0[] System.Array.Empty()'.

2. Generic SQL error.

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=9.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Generic SQL error.Detail:
<OrganizationServiceFault xmlns:i="www.w3.org/.../XMLSchema-instance" xmlns="schemas.microsoft.com/.../Contracts">
<ActivityId>98c8caae-1fc1-4742-8410-92a8777d6512</ActivityId>
<ErrorCode>-2147204784</ErrorCode>
<ErrorDetails xmlns:d2p1="schemas.datacontract.org/.../System.Collections.Generic" />
<Message>Generic SQL error.</Message>
<Timestamp>2018-03-13T17:10:31.7571437Z</Timestamp>
<ExceptionRetriable>false</ExceptionRetriable>
<ExceptionSource i:nil="true" />
<InnerFault i:nil="true" />
<OriginalException i:nil="true" />
<TraceText i:nil="true" />
</OrganizationServiceFault>

can any one please suggest me how to fix this issue. Its very urgent for me.

 Thanks in Advance