The requested page cannot be found error in Joomla

'The requested page cannot be found.' how to resolved this joomla page error.

You may not be able to visit this page because of:
an out-of-date bookmark/favourite
a mistyped address
a search engine that has an out-of-date listing for this site
you have no access to this page

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Home Page

If difficulties persist, please contact the System Administrator of this site and report the error below.

0 SQL=select name, username from demo_users;

Kindly help me to resolve this error.
thanks