use local reference files as fallback

csst_common/data_manager.py

@@ -529,13 +529,16 @@ class CsstMsDataManager:
              'shutter': '/crdsroot/references/msc/csst_msc_ms_shutter_11_000001.fits'}
         """
         if self.crds.is_available:
+            try:
                 print("CRDS available, use refs from CRDS ...")
                 return self.crds.retry(
                     self.crds.get_refs, 3,
                     file_path=self.l0_detector(detector)
                 )
-        else:
-            print("CRDS unavailable, use refs from local files ...")
+            except BaseException as e:
+                print("CRDS reference access failed! ", e)
+
+        print("Use refs from local files ...")
         refs = dict()
         if self.datatype == "mbi":
             ref_types = ["bias", "dark", "ledflat", "shutter"]