Internal Server Error

[Andy1]

I am having problems with an Internal Server Error.

 

I was uploading a CSV file, first of all with just one row to check it worked ok. This didn't cause any problems. Then I uploaded a CSV file with 6 rows and I got the following error:

 

Internal Server Error

 

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

 

Please contact the server administrator, webmaster 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.

 

I have read the the file permissions should be set to 755, which I have tried to do, but do I need co click on every file to change the permission or is there a way of changing everything at once?

 

I was also blocked from the admin area, but that has been sorted by changing the 'public.html' folder to 755.

 

I can't even edit a category or product without getting the ISE.

 

The log says:

 

[sun Jul 24 14:27:40 2011] [error] [client 81.141.142.248] Premature end of script headers: index.php,

 

Please can someone help, I have asked my host but they just told me to change the file permissions and then closed the support ticket.

 

I am tempted to re-install everything again, but I could still have this problem in the future.

 

Thank you for any help.