:) I had the same two problems. I'll attempt to help as best as I can...
Error #1) Couldn't create File: /home/db-int.net/www/blog/wp-content/plugins/post_notification/_temp/post_notification.lock
Please assure the the path is writeable. This is an error!
Answer: This is a chmod situation. At least it was for me. I resolved it by creating the file "post_notification.lock" through a text editor, uploading it to the directory. In your case it would be: /home/db-int.net/www/blog/wp-content/plugins/post_notification/_temp/
Once the file is uploaded, chmod to 777. However, there may be some security issues with chmoding the file to this. So you might want to check that out. You could also try other chmods to see if they'll work.
Error #2) This version of PHP does not support the function mb_check_encoding. You might get some trouble with non-ASCII chars in the subject. Most hosters support this, as it is a sensible php-extension. More information.
Answer: For me, this "seemed" to be Apache related. I added several modules onto Apache and once I rebuilt it the error disappeared. I'm not sure what module it was that corrected the issue but here are the modules I added on:
* Mbstring (this might've been the one that fixed it seeing as it has "MB" as part of the module name)
* Zend Optimizer for PHP
* IonCube Loader for PHP
If indeed it is Apache like it was for me, you need root access (to WHM) to fix this problem. If not, contact your hosting and relay the problem to them and they can update Apache for you in order to fix it.