Your E-junkie account's login password is unrelated to your download link expiration settings, and we do not expire passwords. We also don't generate any error that says "Invalid password", but maybe you're getting a message that says "invalid link" when you try an expired download link?
We issue each buyer their own, unique link that expires after the maximum Attempts or Hours (whichever comes first) that you specify in the product's settings, so even if a buyer shares their link, it will soon expire and become useless to everyone. Every buyer should be using your E-junkie purchase buttons to place an order and obtain their own link. If you want to offer free downloads, you can set the item price at 0.00 and use the Add to Cart button code we provide for that item to let visitors place an order to obtain their link without payment using our Free Checkout:
If you just want to post a direct download link on your site for anyone to download from freely, without requiring them to provide any information or place a free order, you don't need any special download service like E-junkie for that at all. You can simply upload the file to your site and link to it the same way you'd link from one page to another.