Messages App on Macbook Not Responding

[bjs2010uk]

Hi I currently own a Macbook Pro, 13 inch, late 2011 model. Ever since upgrading from Lion to Mountain Lion I have experienced issues with the 'messages' app not responding when I wake up my macbook (this is the app to send imessages). Consequently I have to resort to using force quit on the application, as it slows down my whole system. I have even on occasions left the macbook for 5/10 minutes in hope that the system/app would re-stabilise but I find this makes no difference and my whole system is slow and laggy until I use force quit on the messages app. I know it is this specific app, which is not responding as I have managed to open the activity monitor when experiencing problems.

Please could someone advise me if there is a way to rectify this issue?


Thanks in advance for your help!