diff --git a/resources/MatlabInterface/@JEInterface/setVerbose.m b/resources/MatlabInterface/@JEInterface/setVerbose.m
index 0a87f233..49f585fb 100644
--- a/resources/MatlabInterface/@JEInterface/setVerbose.m
+++ b/resources/MatlabInterface/@JEInterface/setVerbose.m
@@ -2,12 +2,15 @@ function int=setVerbose(int, bOn, varargin)
 % Activate debug output for the MatlabProblem.
 %      setVerbose(JI, bOn [, dbgfile])
 % It is written to a file with given name or to matlabproblem-debug.log 
-% if none is given.
+% if none is given. To switch file names, first deactivate logging.
 %   JI: the interface instance
 %   bOn: 1 activates debug output, 0 deactivates it
 %   dbgfile: optional filename
 %
 
+if (nargin<=1)
+    error('Missing argument!');
+end
 if (nargin > 2)
     if ischar(varargin{1})
         fname=varargin{1};
@@ -17,7 +20,7 @@ if (nargin > 2)
         disp('Invalid third argument, expected char. Using default output file name');
     end
 else
-    fname=null;
+    fname='';
 end
         
 int.mp.setDebugOut( bOn==1, fname);
diff --git a/src/eva2/server/go/problems/MatlabProblem.java b/src/eva2/server/go/problems/MatlabProblem.java
index c4c52034..2a85ddb2 100644
--- a/src/eva2/server/go/problems/MatlabProblem.java
+++ b/src/eva2/server/go/problems/MatlabProblem.java
@@ -140,12 +140,15 @@ public class MatlabProblem extends AbstractOptimizationProblem implements Interf
 	 */
 	public void setDebugOut(boolean swtch, String fname) {
 		TRACE=swtch;
+//		System.err.println("setDebugOut: " +  swtch +" " + fname);
 		if (!swtch && (dos != null)) {
 			dos.close();
 			dos = null;
-		} else if ((dos == null) && swtch) {
+		} else if (swtch && (dos == null)) {
 			try {
-				dos = new PrintStream(new FileOutputStream(fname==null ? defTestOut : fname));
+				if (fname==null || (fname.length()==0)) fname = defTestOut;
+//				System.err.println("Opening "+fname);
+				dos = new PrintStream(new FileOutputStream(fname));
 			} catch (FileNotFoundException e) {
 				e.printStackTrace();
 			}