diff -u -r1.11 -r1.12
--- NonTrivialPFA.java	12 Jul 2007 22:07:19 -0000	1.11
+++ NonTrivialPFA.java	20 Aug 2007 17:41:20 -0000	1.12
@@ -287,7 +287,22 @@

 	    addLikelihoodWriter("likwrite: ", inputClusterList, inputMIPList, inputClumpList, inputHitListsForAssociator, inputClusterListsForAssociator, mcListName);
 	} else {
 	    // Read in likelihood:

-	    LikelihoodEvaluator eval = LikelihoodEvaluator.readFromFile("likelihood.bin");

+	    LikelihoodEvaluator eval = null;
+	    try {
+		eval = LikelihoodEvaluator.readFromFile("likelihood.bin");
+	    } catch (AssertionError x) {
+		System.out.println("ERROR: Failed to read in the likelihood control file <likelihood.bin> from the working directory.");
+		System.out.println("To generate this file, run this Driver in write mode on a similar sample of events.");
+		System.out.println("Read vs write mode is toggled via a switch in the Driver constructor:");
+		System.out.println("    public NonTrivialPFA(boolean writeLikelihood)");
+		System.out.println("To get started quickly, some default files are available on the web. These are tuned for");
+		System.out.println("acme0605-series detectors on 500 GeV (e+e- -> Z1 Z1, Z1 -> nu nubar, Z2 -> qqbar) events.");
+		System.out.println("  http://www.slac.stanford.edu/~mcharles/tmp/sid/acme0605/likelihood.bin");
+		System.out.println("  http://www.slac.stanford.edu/~mcharles/tmp/sid/acme0605_steel_rpc/likelihood.bin");
+		System.out.println("  http://www.slac.stanford.edu/~mcharles/tmp/sid/acme0605_steel_scint/likelihood.bin");
+		System.out.println("  http://www.slac.stanford.edu/~mcharles/tmp/sid/acme0605_w_rpc/likelihood.bin");
+		System.exit(-1);
+	    }

 	    // Some likelihood quantities need per-event info:
 	    makeEventInfoList(eval);
 	    eval.setDebug(false); // lots of debug printout if enabled!