diff --git a/calibre-plugin/__init__.py b/calibre-plugin/__init__.py
index 77a6e2d..fa35047 100644
--- a/calibre-plugin/__init__.py
+++ b/calibre-plugin/__init__.py
@@ -85,8 +85,10 @@ See the "LICENSE" file for a full copy of the GNU GPL v3.
 #          Print useful warning if LicenseServiceCertificate download fails,
 #          fix error with the loan list not being updated when importing multiple ACSMs at once,
 #          fix bug with the GUI extension in non-English environments,
-#          add setting to choose between simultaneous (faster) or sequencial (more ADE-like) 
-#          import of multiple ACSM files
+#          fix softlock when importing a large number of ACSM files at once,
+#          fix "account folder not found" error message on some clean installations,
+#          add experimental support for Calibre 3.48. 
+
 
 
 
@@ -99,7 +101,12 @@ __version__ = PLUGIN_VERSION = ".".join([str(x)for x in PLUGIN_VERSION_TUPLE])
 
 
 from calibre.utils.config import config_dir         # type: ignore
-from calibre.utils.lock import SingleInstance, singleinstance       # type: ignore
+from calibre.utils.lock import singleinstance       # type: ignore
+
+try:
+    from calibre.utils.lock import SingleInstance       # type: ignore
+except:
+    from calibre_plugins.deacsm.singleinstance_helper import SingleInstance
 
 import os, shutil, traceback, sys, time, io, random
 import zipfile
@@ -113,7 +120,7 @@ class ACSMInput(FileTypePlugin):
     supported_platforms         = ['linux', 'osx', 'windows']
     author                      = "Leseratte10"
     version                     = PLUGIN_VERSION_TUPLE
-    minimum_calibre_version     = (4, 0, 0)
+    minimum_calibre_version     = (3, 48, 0)
     file_types                  = set(['acsm'])
     on_import                   = True
     on_preprocess               = True
diff --git a/calibre-plugin/gui_main.py b/calibre-plugin/gui_main.py
index 6817c20..11141b8 100644
--- a/calibre-plugin/gui_main.py
+++ b/calibre-plugin/gui_main.py
@@ -70,7 +70,12 @@ def create_menu_action_unique(ia, parent_menu, menu_text, image=None, tooltip=No
 class ActualACSMInputGUIExtension(InterfaceAction):
     name                        = "ACSM Input Plugin GUI Extension"
     
-    popup_type = QToolButton.ToolButtonPopupMode.InstantPopup
+    try: 
+        popup_type = QToolButton.ToolButtonPopupMode.InstantPopup
+    except AttributeError:
+        # Needed for Calibre 3
+        popup_type = 2
+
     action_type = 'global'
     action_spec = ("ACSM Input", None, "ACSM Input Plugin by Leseratte10", None)
     # Text, icon, tooltip, keyboard shortcut
diff --git a/calibre-plugin/prefs.py b/calibre-plugin/prefs.py
index 3818af8..d8a7576 100644
--- a/calibre-plugin/prefs.py
+++ b/calibre-plugin/prefs.py
@@ -15,7 +15,6 @@ import os
 import traceback
 
 from calibre.utils.config import JSONConfig, config_dir  # type: ignore
-from calibre.constants import iswindows                  # type: ignore
 
 
 class ACSMInput_Prefs():
@@ -54,8 +53,18 @@ class ACSMInput_Prefs():
                 success = True
                 break
 
-        
         if not success:
+            # We did not find an account folder. See if we can create one ...
+            for f in ["DeACSM", "ACSMInput"]:
+                self.__maindir = os.path.join(self.__pluginsdir, f)
+                self.__accountdir = os.path.join(self.__maindir,"account")
+                if os.path.exists(self.__maindir):
+                    os.mkdir(self.__accountdir)
+                    self.deacsmprefs.defaults['path_to_account_data'] = self.__accountdir
+                    success = True
+                    break
+
+        if not success:        
             raise Exception("Why does the account folder not exist?")
             
 
diff --git a/calibre-plugin/singleinstance_helper.py b/calibre-plugin/singleinstance_helper.py
new file mode 100644
index 0000000..e848683
--- /dev/null
+++ b/calibre-plugin/singleinstance_helper.py
@@ -0,0 +1,17 @@
+from calibre.utils.lock import create_single_instance_mutex
+
+class SingleInstance:
+
+    def __init__(self, name):
+        self.name = name
+        self.release_mutex = None
+
+    def __enter__(self):
+        self.release_mutex = create_single_instance_mutex(self.name)
+        return self.release_mutex is not None
+
+    def __exit__(self, *a):
+        if self.release_mutex is not None:
+            self.release_mutex()
+            self.release_mutex = None
+
diff --git a/migration_plugin/__init__.py b/migration_plugin/__init__.py
index 3ed6b48..93c13c1 100644
--- a/migration_plugin/__init__.py
+++ b/migration_plugin/__init__.py
@@ -28,11 +28,9 @@ class DeACSMMigrationPlugin(InterfaceActionBase):
     version                     = (0, 0, 20)
 
     can_be_disabled = False
-    # This plugin will be auto-loaded from the ACSM Input plugin. It doesn't make sense for the user
-    # to disable it. If necessary, the menu bar button can be removed through the Calibre settings.
 
     type = "File type"
-    # Just so that the GUI extension shows up at the same place as the actual ACSM Input plugin.
+    # Just so that the migration extension shows up at the same place as the actual ACSM Input plugin.
 
     try: 
         from calibre.customize import PluginInstallationType