diff --git a/lib/syspro/logon.rb b/lib/syspro/logon.rb
index eb0f1dc..2fddf00 100644
--- a/lib/syspro/logon.rb
+++ b/lib/syspro/logon.rb
@@ -10,6 +10,7 @@ module Syspro
         'CompanyPassword' => company_password
       }
       resp = request(:get, resource_url, params)
+      handle_errors(resp)
       UserIdObject.new(resp[0].http_body)
     end
 
@@ -17,6 +18,11 @@ module Syspro
       '/Logon'
     end
 
+    def handle_errors(resp)
+      body = resp[0].http_body
+      raise AuthenticationError, body if body =~ /^(ERROR)/
+    end
+
     UserIdObject = Struct.new(:guid)
   end
 end
--
libgit2 0.21.4