Gizmo has been working on my forums. I asked him to take a look at a problem with .pdf attachments that give an Adobe error when accessed, while the same .pdf file, transferred to server via ftp is fine.
This started with 7.3.1 and continues with the upgrade to 7.4.1.
I'm linking to two threads that Gizmo tested which show the problem.
Thread 1 Thread 2 
