I've fixed this error so many times and have had to search the internet for the fix everytime that I've finally decided to log it into my own blog. Mainly so I can easily find it.
Here's the problem. As a general rule, all https applications do not cache any pages for security reasons. This leaves the issue of downloading files from a https site. For example, if you try to download a file (pdf, xls, doc, etc) from any site, your computer will download it to cache before opening it with the associated application. So specifically in a Tomcat ssl site, you will get this error (or something like this):
Tomcat is automatic adding a Pragma: no-cache header to your page. Here is the link with the fix.
So where ever the <context> of your web application is defined, you want to add something like this:
<Context>
<Valve className="org.apache.catalina.authenticator.BasicAuthenticator" disableProxyCaching="false" />
</Context>
And of course you can change BasicAuthenticator to FormAuthenticator or DigestAuthenticator depending on what you are using.
Hopes this helps someone.