Internal Server Error with Joomla 1.5.15 Version - Joomla! Forum - community, help and support

hi,
have installed latest version of joomla 1.5.15. after installation, when try administration log in, "internal server error".

message getting
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internal server error

the server encountered internal error or misconfiguration , unable complete request.

please contact server administrator, [no address given] , inform them of time error occurred, , might have done may have caused error.

more information error may available in server error log.
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please guide me how resolve issue ?.

most of these caused files having full write permissions... .htaccess file has 777