ipn_main_handler file missing error but file present

[Bryony]

This is a bit odd - I'm suffering from the oft reported problem with Paypal IPN where the cart does not log an order but the payment goes through properly.

I've read loads of other posts and I've checked the settings as advised. All initially appear correct but here's the thing...

If I visit the url to see if the www.mydomain/ipn_main_handler.php file works, I get a server error telling me the file isn't there.

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, [email protected] 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.

However, it is as I can see it on the server. I've tried overwriting the file to see if some essential part was missing but the problem remains. My error log also reflects this. How can this be?