when i upload inport/export

when i upload the inport/export i have that message on et1049.net/store/admin
Internal Server Error

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

Please contact the server administrator, webmaster@et1049.net and inform them of the time the error occurred, and anything you might have done that may have caused the error.

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

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
and i cant login what i must do pls help

If import/export relates to .csv transfer, be sure that you're using the right version of the utility for your version of OC, and be aware that of several .csv utilities some do not work. Either way, you can throw a 500 (internal error) coupled or not with a 404 (unfound).