If you've customized the default.aspx using Frntpage or something...then you
could try copying the working  -- default.aspx from other server/site and replace
this one...restart/IIS as well...

add ?contents=1 to the end of the page  address. In the list of
webparts that appear, check the box next to the ones that are in
error and delete them.

Fixed it already.......................

office.microsoft.com/.../HA011609351033.aspx

Remove all the Webparts from the page  it take you to and
then add webparts back one by one to see which webpart is creating error.
also u can check LOGS to see what is the problem

Add ?contents=1 at the end of the address of the page  that won't
display. That will display  a page that lists all the webparts on the
page. Those that are causing problems will be identifed, but not by
their name unfortunately. Check the box and delete them.

Unfortunately you can't use SharePoint Designer to edit a page
exhibiting this problem. It refuses to open the page, complaining
that the page has a problem. Well of course it does!

Once you delete the offending webparts you can use SP Designer to
figure out what's missing.

Another option is to temporarily modify the web.config file to allow
error messages to display in the browser. That might me helpful. I
don't remember the three or four parameters you need to change.
Google it.