I'm having a very similar problem to:
Dynamics CRM 2011 - The plug-in type could not be found
Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=7.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.ArgumentNullException: Value cannot be null.
Parameter name: The plug-in type could not be found in the plug-in assembly: Enlighten.CRM.Customisations.Job.CreateJobDetail:
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
<ErrorCode>-2147220970</ErrorCode>
<ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic">
<KeyValuePairOfstringanyType>
<d2p1:key>CallStack</d2p1:key>
<d2p1:value xmlns:d4p1="http://www.w3.org/2001/XMLSchema" i:type="d4p1:string"> at Microsoft.Crm.Sandbox.SandboxAppDomainHelper.Execute(IServiceEndpointNotificationService serviceBusService, IOrganizationServiceFactory organizationServiceFactory, String pluginTypeName, String pluginConfiguration, String pluginSecureConfig, IPluginExecutionContext requestContext)
at Microsoft.Crm.Sandbox.SandboxAppDomainHelper.Execute(IServiceEndpointNotificationService serviceBusService, IOrganizationServiceFactory organizationServiceFactory, String pluginTypeName, String pluginConfiguration, String pluginSecureConfig, IPluginExecutionContext requestContext)
at Microsoft.Crm.Sandbox.SandboxWorker.Execute(SandboxCallInfo callInfo, SandboxPluginExecutionContext requestContext, Guid pluginAssemblyId, Int32 sourceHash, String assemblyName, Guid pluginTypeId, String pluginTypeName, String pluginConfiguration, String pluginSecureConfig, SandboxRequestCounter& workerCounter)</d2p1:value>
</KeyValuePairOfstringanyType>
</ErrorDetails>
<Message>System.ArgumentNullException: Value cannot be null.
Parameter name: The plug-in type could not be found in the plug-in assembly: Enlighten.CRM.Customisations.Job.CreateJob</Message>
<Timestamp>2015-07-23T23:32:27.2903692Z</Timestamp>
<InnerFault i:nil="true" />
<TraceText>
[Enlighten.CRM.Customisations.Job.Deploy: Enlighten.CRM.Customisations.Job.CreateJob]
[d2c5efd5-452b-e511-80c4-00155d00461a: Opportunity Create]
</TraceText>
</OrganizationServiceFault>
This is an existing plugin that I have working in CRM 2011. The main difference is that I've updated the SDK to be against 7.0.0.1 using the nuget package.
https://www.nuget.org/packages/Microsoft.CrmSdk.Extensions/7.0.0.1
The previous question suggested that it was version differences but as far as I can tell my deployment is a newer version if anything (as seen below in the deployment manager below) so the SDK version shouldn't be a problem.
Any ideas?