Error when trying to create a new workflow or dialog.

After updating a custom assembly with a new custom workflow activity, I started receiving this error message:

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.Xaml.XamlObjectReaderException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #E0E42D62Detail: 
<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" />
  <Message>System.Xaml.XamlObjectReaderException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #E0E42D62</Message>
  <Timestamp>2013-09-20T09:25:59.627284Z</Timestamp>
  <InnerFault>
    <ErrorCode>-2147220970</ErrorCode>
    <ErrorDetails xmlns:d3p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
    <Message>System.TypeLoadException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #27E19E0D</Message>
    <Timestamp>2013-09-20T09:25:59.627284Z</Timestamp>
    <InnerFault i:nil="true" />
    <TraceText i:nil="true" />
  </InnerFault>
  <TraceText i:nil="true" />
</OrganizationServiceFault>

After trying a few things such as updating the assembly again with the changes reversed, the same error persisted.

At this stage I decided to take drastic action to get back up and running - clients waiting and all - I deleted all dialogs and workflows using my custom activities and the removed the errant assembly completely from Dynamics.

Then after adding the assembly back in (at this stage were using code that worked in the past), I tried again only to get the same error.

Getting worried now, I have removed the assembly and not added it back in. I continue to get the error above when trying to create a new workflow or dialog.

I am using a local installation of Dynamics CRM 2011 RU 14 and the assemblies are being registered then added to an unmanaged solution.

My hunch is that my errant assembly is still lingering somewhere although it does not appear in the Solution window or the Plugin Registration tool.

Any ideas what I have broken and more importantly how I can fix it?

Thanks,

Ant