App.c:1018 ast_lock_path: Failed to lock path '/var/spool

Hi,
Hope you all will be fine.When i leave a message for say extension 220 and then try to listen the recorded message asterisk show this message.

Also when asterisk say that you have i new email message press 1 to listen the message and after pressing 1 asterisk take a lot of time to play the message and also the voice of the playing message is very low. Also asterisk don’t tell that you receive message on this date. After pressing 1 asterisk take a lot of time and then say message from unknown caller and then play message in very low volume.

So First question is what this warning message mean and why it is coming and how i overcome it because earlier this message didn’t come.
Second why asterisk take so much time in playing message and also why it’s not telling that you receive message on this date.
Third how i increase the volume of the message i.e, when asterisk playing message it will be loud and clear.
I am using asterisk 1.4.18.1. One thing more is it possible for me to update my asterisk to asterisk 1.6. Will updating effect any of mine asterisk 1.4.18.1 settings ? .

Thanks.