diff --git a/cps/config_sql.py b/cps/config_sql.py
index a3798765..9dc0abdd 100644
--- a/cps/config_sql.py
+++ b/cps/config_sql.py
@@ -278,8 +278,7 @@ class _ConfigSQL(object):
             if binary in constants.SUPPORTED_CALIBRE_BINARIES:
                 return os.path.join(binariesdir, binary)
             else:
-                # TODO: Error handling
-                pass
+                raise ValueError("'{}' is not a supported Calibre binary".format(binary))
         return ""
 
     def set_from_dictionary(self, dictionary, field, convertor=None, default=None, encode=None):
diff --git a/cps/helper.py b/cps/helper.py
index aba18dcc..31b15eb9 100644
--- a/cps/helper.py
+++ b/cps/helper.py
@@ -952,7 +952,8 @@ def check_calibre(calibre_location):
 
     try:
         supported_binary_paths = [os.path.join(calibre_location, binary) for binary in SUPPORTED_CALIBRE_BINARIES]
-        if all(os.path.isfile(binary_path) and os.access(binary_path, os.X_OK) for binary_path in supported_binary_paths):
+        binaries_available=[os.path.isfile(binary_path) and os.access(binary_path, os.X_OK) for binary_path in supported_binary_paths]
+        if all(binaries_available):
             values = [process_wait([binary_path, "--version"], pattern='\(calibre (.*)\)') for binary_path in supported_binary_paths]
             if all(values):
                 version = values[0].group(1)
@@ -960,7 +961,8 @@ def check_calibre(calibre_location):
             else:
                 return _('Calibre binaries not viable')
         else:
-            return _('Missing calibre binaries in the specified directory')
+            missing_binaries=[path for path, available in zip(SUPPORTED_CALIBRE_BINARIES, binaries_available) if not available]
+            return _('Missing calibre binaries: %(missing)s', missing=", ".join(missing_binaries))
 
     except (OSError, UnicodeDecodeError) as err:
         log.error_or_exception(err)
diff --git a/cps/tasks/convert.py b/cps/tasks/convert.py
index 74455837..1c9975e1 100644
--- a/cps/tasks/convert.py
+++ b/cps/tasks/convert.py
@@ -233,18 +233,19 @@ class TaskConvert(CalibreTask):
             # windows py2.7 encode as string with quotes empty element for parameters is okay
             # windows py 3.x no encode and as string with quotes empty element for parameters is okay
             # separate handling for windows and linux
-            quotes = [1, 2]
 
-            # TODO: Clean up.
-            # TODO: Maybe delete/clean-up tmp files directly.
+            quotes = [3, 5]
             tmp_dir = os.path.join(gettempdir(), 'calibre_web')
+            if not os.path.isdir(tmp_dir):
+                os.mkdir(tmp_dir)
             calibredb_binarypath = config.get_calibre_binarypath("calibredb")
             opf_command = [calibredb_binarypath, 'show_metadata', '--as-opf', str(book_id), '--with-library', config.config_calibre_dir]
-            p = process_open(opf_command)
+            p = process_open(opf_command, quotes)
             path_tmp_opf = os.path.join(tmp_dir, "metadata_" + str(current_milli_time()) + ".opf")
             with open(path_tmp_opf, 'w') as fd:
                 copyfileobj(p.stdout, fd)
 
+            quotes = [1, 2, 4, 6]
             command = [config.config_converterpath, (file_path + format_old_ext),
                        (file_path + format_new_ext), '--from-opf', path_tmp_opf,
                        '--cover', os.path.join(os.path.dirname(file_path), 'cover.jpg')]
@@ -257,7 +258,7 @@ class TaskConvert(CalibreTask):
                     quotes_index += 1
 
             p = process_open(command, quotes, newlines=False)
-        except OSError as e:
+        except (ValueError, OSError) as e:
             return 1, N_(u"Ebook-converter failed: %(error)s", error=e)
 
         while p.poll() is None: