diff --git a/sylk/configuration/settings.py b/sylk/configuration/settings.py
index 2cb1848..02939c6 100644
--- a/sylk/configuration/settings.py
+++ b/sylk/configuration/settings.py
@@ -1,120 +1,122 @@
 # Copyright (C) 2010-2011 AG Projects. See LICENSE for details.
 #
 
 """
 SIP SIMPLE SDK settings extensions.
 """
 
 __all__ = ['AccountExtension', 'BonjourAccountExtension', 'SylkServerSettingsExtension']
 
+import os
+
 from sipsimple.account import MSRPSettings as AccountMSRPSettings, NATTraversalSettings as AccountNATTraversalSettings
 from sipsimple.account import RTPSettings as AccountRTPSettings, SIPSettings as AccountSIPSettings, TLSSettings as AccountTLSSettings
 from sipsimple.configuration import CorrelatedSetting, Setting, SettingsObjectExtension
 from sipsimple.configuration.datatypes import AudioCodecList, MSRPTransport, NonNegativeInteger, Path, Port, PortRange, SampleRate, SIPTransportList, SRTPEncryption
 from sipsimple.configuration.settings import AudioSettings, LogsSettings, RTPSettings, SIPSettings, TLSSettings
 
 from sylk import __version__ as server_version
 from sylk.configuration import ServerConfig, SIPConfig, MSRPConfig, RTPConfig
 
 
 # Account settings extensions
 
 msrp_transport = 'tls' if MSRPConfig.use_tls else 'tcp'
 class AccountMSRPSettingsExtension(AccountMSRPSettings):
     transport = Setting(type=MSRPTransport, default=msrp_transport)
 
 class AccountNATTraversalSettingsExtension(AccountNATTraversalSettings):
     use_msrp_relay_for_inbound = Setting(type=bool, default=False)
     use_msrp_relay_for_outbound = Setting(type=bool, default=False)
 
 
 class AccountRTPSettingsExtension(AccountRTPSettings):
     audio_codec_list = Setting(type=AudioCodecList, default=RTPConfig.audio_codecs, nillable=True)
     srtp_encryption = Setting(type=SRTPEncryption, default=RTPConfig.srtp_encryption)
     use_srtp_without_tls = Setting(type=bool, default=True)
 
 
 class AccountSIPSettingsExtension(AccountSIPSettings):
     register = Setting(type=bool, default=False)
 
 
-tls_certificate = Path(ServerConfig.certificate) if ServerConfig.certificate else None
+tls_certificate = Path(ServerConfig.certificate) if ServerConfig.certificate and os.path.isfile(ServerConfig.certificate) else None
 class AccountTLSSettingsExtension(AccountTLSSettings):
     certificate = Setting(type=Path, default=tls_certificate, nillable=True)
     verify_server = Setting(type=bool, default=ServerConfig.verify_server)
 
 class AccountExtension(SettingsObjectExtension):
     enabled = Setting(type=bool, default=True)
 
     msrp = AccountMSRPSettingsExtension
     nat_traversal = AccountNATTraversalSettingsExtension
     rtp = AccountRTPSettingsExtension
     sip = AccountSIPSettingsExtension
     tls = AccountTLSSettingsExtension
 
 
 class BonjourAccountExtension(SettingsObjectExtension):
     enabled = Setting(type=bool, default=False)
 
 
 
 # General settings extensions
 
 class AudioSettingsExtension(AudioSettings):
     input_device = Setting(type=str, default=None, nillable=True)
     output_device = Setting(type=str, default=None, nillable=True)
     sample_rate = Setting(type=SampleRate, default=16000)
 
 
 log_directory = Path(ServerConfig.trace_dir) if ServerConfig.trace_dir else None
 class LogsSettingsExtension(LogsSettings):
     directory = Setting(type=Path, default=log_directory)
     trace_sip = Setting(type=bool, default=ServerConfig.trace_sip)
     trace_msrp = Setting(type=bool, default=ServerConfig.trace_msrp)
     trace_pjsip = Setting(type=bool, default=False)
     trace_notifications = Setting(type=bool, default=ServerConfig.trace_notifications)
 
 
 class RTPSettingsExtension(RTPSettings):
     port_range = Setting(type=PortRange, default=PortRange(RTPConfig.port_range.start, RTPConfig.port_range.end))
     timeout = Setting(type=NonNegativeInteger, default=RTPConfig.timeout)
 
 
 def sip_port_validator(port, sibling_port):                                                                                                                                                  
     if port == sibling_port != 0:
         raise ValueError("the TCP and TLS ports must be different")
 
 transport_list = []
 if SIPConfig.local_udp_port:
     transport_list.append('udp')
 if SIPConfig.local_tcp_port:
     transport_list.append('tcp')
 if SIPConfig.local_tls_port:
     transport_list.append('tls')
 
 udp_port = SIPConfig.local_udp_port or 0
 tcp_port = SIPConfig.local_tcp_port or 0
 tls_port = SIPConfig.local_tls_port or 0
 
 class SIPSettingsExtension(SIPSettings):
     udp_port = Setting(type=Port, default=udp_port)
     tcp_port = CorrelatedSetting(type=Port, sibling='tls_port', validator=sip_port_validator, default=tcp_port)
     tls_port = CorrelatedSetting(type=Port, sibling='tcp_port', validator=sip_port_validator, default=tls_port)
     transport_list = Setting(type=SIPTransportList, default=transport_list)
 
 
-ca_list = Path(ServerConfig.ca_file) if ServerConfig.ca_file else None
+ca_list = Path(ServerConfig.ca_file) if ServerConfig.ca_file and os.path.isfile(ServerConfig.ca_file) else None
 class TLSSettingsExtension(TLSSettings):
     ca_list = Setting(type=Path, default=ca_list, nillable=True)
 
 
 class SylkServerSettingsExtension(SettingsObjectExtension):
     user_agent = Setting(type=str, default='SylkServer-%s' % server_version)
 
     audio = AudioSettingsExtension
     logs = LogsSettingsExtension
     rtp = RTPSettingsExtension
     sip = SIPSettingsExtension
     tls = TLSSettingsExtension