having 404 problem with custom post types

My client has created custom post type as “events” and he added couple of pages under this events page template as “events overview”, “annual-events(this page is combination of all the events created under the events category)”, “host a private event” etc. He also created lot of events(annual) under this section. The problem is if I use the default permalink everything works fine but if I use the permalink as “Numeric archive”(as my client wants that structure) none of the event pages(which follows the event template) “annual-events”, “host a private event” etc are working. They are getting 404 error, but the annual-events like “birthday party” etc are working.
for example:

http://www.sitename.org/events/overview — is not working

http://www.sitename.org/events/host-a-private-event –is not working

but

http://www.sitename.org/events/ciara’s-butterfly-bash — is working

I am sure there may be some problem with .htaccess file. Can anyone help me with this?