[Plugin: WP Post Notifier For All] Wp Post Notifier for All not working after upgrade

Hi,
I wonder if can get some help. I have self hosted wordpress blog. The blog was in the version 3.1.2. I upgraded it to 3.3.2. the blog has Wp Post Notifier for All plugin installed in it which was working fine before upgrade. After the upgrade the plugin seems to send new post notifications to few registered users but not to all of the registered users. And those users who are recieving notifications dont recieve notifications every time a new post is published. So its working partly. Also, after the upgrade some users cant see the publish button.
Are these two problems being faced linked to each other? I have tried the folling possible solutions to sort out these problems:
1. Tried to deactivate other plugins in the blog and see if post notifier plugin works.
2. Deleted the Post notifier plugin and installed it again but this did not work either.
3. Created a test blog which is in the same version as my blog and installed all the plugins which my blog has on the test blog. My test blog works perfectly fine sending notifications to all registered users. So, this is isn’t a compatibility issue either.
4. Tried to do a bit more research in Google. Found a link
http://faycaltirich.blogspot.co.uk/1979/01/wp-post-notifier-for-all.html which explains few things which can be tried to fix the problem but did not work for me.
5. I installed one more plugin called Email Log which actually logs all the emails sent out from my blog. I can see in the log that the Email is actually being sent out from the blog but not recieved by the users.
6. I have also checked if the emails are actually blocked by the server but that is not the case either.
I am unable to figure out what might be the problem. Please help

http://wordpress.org/extend/plugins/wp-post-notifier-for-all/