This patch fixes two bugs:
1. It ignores an device open failure if polling.
2. It disables the insanity check on reading the 
   tape label while polling. Normally the check
   doesn't allow the label to be read more than 100
   times.

Apply the patch to version 1.34.6 (possibly earlier versions) with:

 cd <bacula-source>
 patch -p0 <1.34.6-poll.patch
 make
 ...

Index: src/stored/label.c
===================================================================
RCS file: /cvsroot/bacula/bacula/src/stored/label.c,v
retrieving revision 1.42.2.1
diff -u -r1.42.2.1 label.c
--- src/stored/label.c	20 Jun 2004 11:43:04 -0000	1.42.2.1
+++ src/stored/label.c	2 Sep 2004 12:21:00 -0000
@@ -74,8 +74,8 @@
 	  * Cancel Job if too many label errors
 	  *  => we are in a loop
 	  */
-	 if (jcr->label_errors++ > 100) {
-            Jmsg(jcr, M_FATAL, 0, "%s", jcr->errmsg);
+	 if (!dev->poll && jcr->label_errors++ > 100) {
+            Jmsg(jcr, M_FATAL, 0, "Too many tries: %s", jcr->errmsg);
 	 }
 	 return jcr->label_status = VOL_NAME_ERROR;
       }
@@ -157,8 +157,8 @@
        * Cancel Job if too many label errors
        *  => we are in a loop
        */
-      if (jcr->label_errors++ > 100) {
-         Jmsg(jcr, M_FATAL, 0, "%s", jcr->errmsg);
+      if (!dev->poll && jcr->label_errors++ > 100) {
+         Jmsg(jcr, M_FATAL, 0, "Too many tries: %s", jcr->errmsg);
       }
       return jcr->label_status = VOL_NAME_ERROR;
    }
Index: src/stored/mount.c
===================================================================
RCS file: /cvsroot/bacula/bacula/src/stored/mount.c,v
retrieving revision 1.59.2.1
diff -u -r1.59.2.1 mount.c
--- src/stored/mount.c	20 Jun 2004 11:43:04 -0000	1.59.2.1
+++ src/stored/mount.c	2 Sep 2004 12:21:00 -0000
@@ -154,7 +154,11 @@
 
    /* Ensure the device is open */
    if (!open_device(jcr, dev)) {
-      return 0;
+      if (dev->poll) {
+	 goto mount_next_vol;
+      } else {
+	 return 0;
+      }
    }
 
    /*