WHen we install phpbb SEO advance rewrite mod it show only index page link in viewonline.php.. how to resolve the issue?

Do you have this set to "No" in the ACL? (under "Load settings") If so, the URLs will always point to the forum index.

Show user’s activity:
Displays active topic/forum in user profiles and user control panel. It is recommended to disable this on boards with more than one million posts.

Only Two things set to No in server configuration -> load setting
Enable topic marking for guests: No
Recompile stale style components: No

The 0.4.0 mod rewrite are breaking a bit of the online listing tracking, user will never appear as browsing a forum, it's only working when virtual folder is on and forum id removing is off.

This is fixed in 0.4.2 (already in the 3.0.1 premod), but it will only be able to do as much as phpBB3, forum are only detected as being visited when the url loaded includes the forum id, so urls like viewtopic.php?t=xx will not provide with the forum id, same for topicxx.html or topic-title-txx.html.
It's working in all other cases.

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Where i can download 0.4.2 for phpbb 3.01?

It will be released soon, today probably, subscribe to the release thread to be notified by mail

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