Index: openacs-4/packages/xowiki/tcl/xowiki-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/xowiki/tcl/xowiki-procs.tcl,v
diff -u -r1.542.2.167 -r1.542.2.168
--- openacs-4/packages/xowiki/tcl/xowiki-procs.tcl	15 Dec 2022 19:30:02 -0000	1.542.2.167
+++ openacs-4/packages/xowiki/tcl/xowiki-procs.tcl	24 Dec 2022 16:33:24 -0000	1.542.2.168
@@ -2925,7 +2925,15 @@
         set success 0
       }
     } else {
-      set errorMsg [_ xowiki.Page-validate_name-duplicate_item [list value $name]]
+      #
+      # The plain form valudation has signaled, that the name is not
+      # ok. Try to provide a more detailed error message.
+      #
+      if {![:istype ::xowiki::File] && [regexp {^[a-zA-Z][a-zA-Z]:$} $name]} {
+        set errorMsg [_ xowiki.Page-validate_name-invalid_name [list value $name]]
+      } else {
+        set errorMsg [_ xowiki.Page-validate_name-duplicate_item [list value $name]]
+      }
     }
 
     if {$success} {