diff --git a/gui/Gui/Scytherthread.py b/gui/Gui/Scytherthread.py
index dc8338d..d3272ea 100644
--- a/gui/Gui/Scytherthread.py
+++ b/gui/Gui/Scytherthread.py
@@ -60,7 +60,12 @@ class ScytherThread(threading.Thread):
         scyther.setInput(self.spdl)
 
         # verification start
-        claims = scyther.verify()
+        try:
+            claims = scyther.verify()
+        except Scyther.Error.ScytherError, el:
+            claims = None
+            pass
+
         summary = str(scyther)
 
         return (scyther, claims, summary)
diff --git a/gui/Scyther/Error.py b/gui/Scyther/Error.py
index 1ab5718..d498a35 100644
--- a/gui/Scyther/Error.py
+++ b/gui/Scyther/Error.py
@@ -9,6 +9,22 @@ class Error(Exception):
     """Base class for exceptions in this module."""
     pass
 
+class ScytherError(Error):
+    """Exception raised for errors generated by the backend
+
+    Attributes:
+        errorlist -- list of error lines are retrieved from the
+        backend
+    """
+
+    def __init__(self, errorlist):
+        self.errorlist = errorlist
+
+    def __str__(self):
+        s = "Scyther backend reported the following errors:\n"
+        s = s + "\n".join(self.errorlist)
+        return s
+
 class InputError(Error):
     """Exception raised for errors in the input.
 
diff --git a/gui/Scyther/Scyther.py b/gui/Scyther/Scyther.py
index 3c8b551..c1c06c5 100755
--- a/gui/Scyther/Scyther.py
+++ b/gui/Scyther/Scyther.py
@@ -193,9 +193,9 @@ class Scyther(object):
             raise Error.NoBinaryError
 
         # Sanitize input somewhat
-        if not spdl or spdl == "":
+        if spdl == "":
             # Scyther hickups on completely empty input
-            spdl = None
+            spdl = "\n"
 
         # Generate temporary files for the output.
         # Requires Python 2.3 though.
@@ -275,19 +275,22 @@ class Scyther(object):
         self.warnings = []
         for l in errors.splitlines():
             line = l.strip()
-            # filter out any non-errors (say maybe only claim etc) and count
-            # them.
-            if line.startswith("claim\t"):
-                # Claims are lost, reconstructed from the XML output
-                continue
-            if line.startswith("warning"):
-                # Warnings are stored seperately
-                self.warnings.append(line)
-                continue
-            # otherwise it is an error
-            self.errors.append(line)
+            if len(line) > 0:
+                # filter out any non-errors (say maybe only claim etc) and count
+                # them.
+                if line.startswith("claim\t"):
+                    # Claims are lost, reconstructed from the XML output
+                    continue
+                if line.startswith("warning"):
+                    # Warnings are stored seperately
+                    self.warnings.append(line)
+                    continue
+                # otherwise it is an error
+                self.errors.append(line)
 
         self.errorcount = len(self.errors)
+        if self.errorcount > 0:
+            raise Error.ScytherError(self.errors)
 
         # process output
         self.output = output
@@ -310,14 +313,19 @@ class Scyther(object):
         else:
             return self.output
 
-    def verifyOne(self,cl):
+    def verifyOne(self,cl=None):
         """
         Verify just a single claim with an ID retrieved from the
         procedure below, 'scanClaims', or a full claim object
         """
-        if isinstance(cl,Claim.Claim):
-            cl = cl.id
-        return self.verify("--filter=%s" % cl)
+        if cl:
+            # We accept either a claim or a claim id
+            if isinstance(cl,Claim.Claim):
+                cl = cl.id
+            return self.verify("--filter=%s" % cl)
+        else:
+            # If no claim, then its just normal verification
+            return self.verify()
 
     def scanClaims(self):
         """
diff --git a/gui/mpa.py b/gui/mpa.py
index a3aff20..90c8fa6 100755
--- a/gui/mpa.py
+++ b/gui/mpa.py
@@ -8,9 +8,11 @@ Scyther Python API (contained in the Scyther subdirectory)
 In this example, multi-protocol attack analysis is performed on a small
 test set.
 
+Author: Cas Cremers
+
 """
 
-import Scyther.Scyther as Scyther
+from Scyther import Scyther
 
 def MyScyther(protocollist,filter=None):
     """
@@ -19,12 +21,11 @@ def MyScyther(protocollist,filter=None):
     will be evaluated.
     """
     s = Scyther.Scyther()
+    # untyped matching
     s.options = "--match=2"
-    if filter:
-        s.options += " --filter=%s" % (filter)
     for protocol in protocollist:
         s.addFile(protocol)
-    s.verify()
+    s.verifyOne(filter)
     return s
     
 
@@ -42,11 +43,10 @@ def getCorrectIsolatedClaims(protocolset):
         # verify protocol in isolation
         s = MyScyther([protocol])
         # investigate the results
-        if not s.errors:
-            goodprotocols.append(protocol)
-            for claim in s.claims:
-                if claim.okay:
-                    correctclaims.append((protocol,claim.id))
+        goodprotocols.append(protocol)
+        for claim in s.claims:
+            if claim.okay:
+                correctclaims.append((protocol,claim.id))
     return (goodprotocols,correctclaims)
 
 def verifyMPAlist(mpalist,claimid):
@@ -124,7 +124,7 @@ def findAllMPA(protocolset,maxcount=3):
         findMPA(protocolset,protocol,claimid,maxcount=3)
 
 
-if __name__ == '__main__':
+def main():
     """
     Simple test case with a few protocols
     """
@@ -137,5 +137,8 @@ if __name__ == '__main__':
     print "Analysis complete."
 
 
+if __name__ == '__main__':
+    main()
 
 
+# vim: set ts=4 sw=4 et list lcs=tab\:>-:
diff --git a/gui/scyther-gui.py b/gui/scyther-gui.py
index 66d30c3..c34f60d 100755
--- a/gui/scyther-gui.py
+++ b/gui/scyther-gui.py
@@ -24,11 +24,8 @@ from optparse import OptionParser, SUPPRESS_HELP
 #---------------------------------------------------------------------------
 
 """ Import scyther-gui components """
-import Gui.About as About
-import Gui.Preference as Preference
-import Gui.Mainwindow as Mainwindow
-import Gui.Misc as Misc
-import Scyther.Scyther as Scyther
+from Gui import About,Preference,Mainwindow,Misc
+from Scyther import Scyther
 
 #---------------------------------------------------------------------------