The only thing that might be different are some user settings. Perhaps someone needs to observe a few transactions and be a second set of eyes?

Um, I can tell you the same errors don't occur with anyone else or on a different system, nor do they occur consistently on this specific system he's "accusing".  I have to go with what Walter says, that it's a PC (and not the person) that's causing the problem, and investigate it.    Ok, so I'm asking if anyone else has experience this issue before, where a PC actually causes problems in Evo.

Yes, I've seen a workstation cause problems but never that specific.  
 
In addition to the other great suggestions here, I'd probably try:  
 
• Copy the ISTS folder from a working workstation or clear and reinstall the Evo client.
• If you have a server that supports Terminal Services maybe you can set your user up to try Evo right at the server...with adult supervision if the problem follows.
 
Can your user repeat the steps that cause the error(s)?