After purchasing a downloadable product, the order is recorded and notices are sent ok. Login to deliver.php is successful, but when the Download button is clicked a message "Invalid username or password..." appears.
First, check that the $ahsopurl is correct in config.inc.php.
Note: Some new versions of AShop Software now have automatic URL setting within the install.php script. There will not be a path variable setting within config.inc.php for these versions. If this is the case, all of the configuration settings are now stored within the database table 'preferences', which can be managed by using a free program named phpMyAdmin. This program or something similar is included with most virtual hosting services.
Look at the URL in the address bar when logging into deliver.php. If the URL changes from http://www.yourdomain.com to http://yourdomain.com or visa-versa, this is probably the cause. This happens due to misconfiguration of the domain name server. Changing the config.inc setting to match the format that it is changing to may fix the problem, but the best way is to get your hosting company to fix the domain name server settings.