Feature Event Receiver Error

I have an event receiver that is looping through a group of lists and associating a workflow to it if they have content approval enabled. The feature fails to activate with this error:

Error occurred in deployment step ‘Activate Features’: Collection was modified; enumeration operation may not execute.

Here is the code snippet. If I comment out the line in bold, it activates without error:

public override void FeatureActivated(SPFeatureReceiverProperties properties)
{
     using (SPSite site = properties.Feature.Parent as SPSite)
     {
          using (SPWeb web = site.OpenWeb(“/marketingdc”))
          {
               SPWorkflowTemplate wfTemplate = web.WorkflowTemplates.GetTemplateByName(“CPMDApproval”, web.Locale);
               SPList tasks = web.Lists[“Tasks”];
               SPList wfHistory = web.Lists[“Workflow History”];
               foreach (SPList list in web.Lists.Cast<SPList>().Where(l => l.EnableModeration == true))
               {
                    SPWorkflowAssociation wfAssociation = list.WorkflowAssociations.GetAssociationByName(“Marketing Docs Approval”, web.Locale);
                    if (wfAssociation == null)
                    {
                         wfAssociation = SPWorkflowAssociation.CreateListAssociation(wfTemplate, “Marketing Docs Approval”, tasks, wfHistory);
                         wfAssociation.AllowManual = true;
                         wfAssociation.AutoStartChange = false;
                         wfAssociation.AutoStartCreate = false;
                         list.WorkflowAssociations.Add(wfAssociation);
                    }
                    else
                    {
                         wfAssociation.AllowManual = true;
                         wfAssociation.AutoStartChange = false;
                         wfAssociation.AutoStartCreate = false;
                         list.WorkflowAssociations.Update(wfAssociation);
                    }
               }
          }
     }
}