VBA does not allow a time string "0:0:0".

This is a workaround patch. In ProjectConnector::addMilestone

     If due <> "" And due <> "0" Then    '基準計画の開始日を設定
-         t.Start = due
-        t.BaselineStart = due
+         t.Start = Replace(due, " 0:0:0", " 00:00:00")
+        t.BaselineStart = Replace(due, " 0:0:0", " 00:00:00")
         t.BaselineDuration = 0
     End If
    
    t.Duration = 0 'あえて期間を0として気づきやすくする
     If completed <> "" And completed <> "0" Then    '開始日を設定
          t.PercentComplete = 100
-        t.Start = completed
+        t.Start = Replace(completed, " 0:0:0", " 00:00:00")
         memo = memo + "実:" + completed + vbCrLf
     End If

This may be correct patch.
In TracXMLRPC::convertDateStr

-    convertDateStr = Format(d, "yyyy/mm/dd h:m:s")
+    convertDateStr = Format(d, "yyyy/mm/dd hh:mm:ss")