cannot uninstall managed solution

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=7.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Should be exactly 1 MessageProcessingStep registered for workflowDetail: 
<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>Should be exactly 1 MessageProcessingStep registered for workflow</Message>
  <Timestamp>2015-04-08T15:10:48.3626414Z</Timestamp>
  <InnerFault i:nil="true" />
  <TraceText i:nil="true" />
</OrganizationServiceFault>