gistfile1.txt

private void AddError (Project prj, string text, TaskErrorCategory category)
{
IVsSolution solution = (IVsSolution)package.GetVSService (typeof (IVsSolution));
IVsHierarchy hierarchy = null;

if (prj != null)
solution.GetProjectOfUniqueName (prj.UniqueName, out hierarchy);

ErrorTask task = new ErrorTask ();

task.Text = text;
task.ErrorCategory = category;
task.HierarchyItem = hierarchy;

package.ErrorListProvider.AddTask (text, (int)category, hierarchy);
}