Unable to install any demo data.

This is the message that I get when I do the manual update. I have tried the automatic as instructed in the instructions, but that always fails. I am trying to install the main demo. This last time I started from scratch, removed all including WordPress and reinstalled it again, only tried the manual import this last time. Can you please help?
Thank you.

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.