Thought I would throw this out here in case someone has seen this issue. I must admit it has driven me nuts the last couple days. And the Google searches haven't pulled up anything that quite matches the problem.
Drupal 6.26, Print 6.x-1.18, TCPDF (tried other libraries without making a difference in results)
The project was to add Print module to grant share by email and PDF version to the site. Print Friendly had been added by a previous developer/admin.
The basic problem is that Print Friendly Page, Email to a Friend work great.
The PDF version only works for authenticated users of the site. Anonymous visitor gets a 404 file not found error.
The problem exists on both the live and test servers. I have been playing around on the test server and checked every crevice I can think of in terms of permissions and modules that may be inferring. I have disabled Content Access, given insane levels of permissions in Drupal just to see if it made a difference, bumped up PHP memory limits, completely re-installed modules, and so forth.
I only got about 6 months of Drupal experience under my belt. So thought I would throw this out to see if any more experienced folks might have a quick idea.