diff --git a/PROMS/Volian.Controls.Library/DisplayTabControl.cs b/PROMS/Volian.Controls.Library/DisplayTabControl.cs
index 855f07be..80fd7c14 100644
--- a/PROMS/Volian.Controls.Library/DisplayTabControl.cs
+++ b/PROMS/Volian.Controls.Library/DisplayTabControl.cs
@@ -499,6 +499,11 @@ namespace Volian.Controls.Library
 						dotNetBarManager1.Bars.Remove(bar);
 					ActivateRemainingTab();
 				}
+				// B2018-123 the last tab in the main window was closed.
+				//           remove the procedure version id from the _AllDTCs dictionary
+				//           reset VersionID to zero so that we know the main window is available
+				_AllDTCs.Remove(VersionID);
+				VersionID = 0;
 			}
 			else
 			{